The first Union Pacific Railroad was incorporated on July 1, 1862, under the Pacific Railroad Act of 1862 approved by President Abraham Lincoln. It aimed to construct railroads from the Missouri River to the Pacific as a war measure for the preservation of the Union.

John A. Dix held the position of President of a certain organization from October 1863 to 1865.

Oliver Ames served as the President of a certain organization from 1865 to 1871.

Omaha National Bank served as the registrar for the initial issuance of Union Pacific Corporation stock. Bank officials verified and signed each corporation certificate of registrar, processing approximately 27,000,000 shares of stock.

In May 1869, Union Pacific connected with Central Pacific at Promontory, Utah. This significant event marked the completion of the first transcontinental railroad in the United States.

Thomas A. Scott was in office as the President of a certain organization from April 1871 to March 1872.

Horace F. Clark served as the President of a certain organization from March 1872 to June 1873.

John Duff held the position of President of a certain organization from June 1873 to March 1874.

Sidney Dillon served as the President of a certain organization from March 1874 to June 1884.

Jay Gould signed traffic agreements to consolidate freight, passenger, and express business on Union Pacific and Kansas Pacific Railway, operating the two roads as a single route.

Colorado Central Railroad was leased to Union Pacific Railroad for 50 years.

Jay Gould and his investor associates agreed to purchase controlling interest in the Kansas Pacific Railway, which had been in receivership since November 1876.

Kansas Pacific formally reorganized and removed from receivership.

Union Pacific Railroad was consolidated with Kansas Pacific Railway and Denver Pacific Railway on January 24, 1880 to form the Union Pacific Railway. Jay Gould controlled all three railroads.

Standard Time, proposed by the nation's railroads, is adopted throughout the United States.

Charles F. Adams was in office as the President of a certain organization from June 1884 to November 1890.

The Interstate Commerce Commission, the nation's first independent regulatory agency, was established to oversee railroads.

Sidney Dillon held the position of President of a certain organization from November 1890 to April 1892.

Silas H.H. Clark served as the President of a certain organization from June 1892 to June 1897.

On October 13, 1893, Union Pacific Railway declared bankruptcy and was placed under the control of an independent receiver, reflecting the economic challenges faced by the company during the Panic of 1893.

In July 1897, Union Pacific Railroad (UP) was incorporated as a reorganization of Union Pacific Railway, which had been in receivership since 1893. The company operated all UP lines in Nebraska, Kansas, Colorado, and Wyoming, extending into Ogden, Utah.

On January 22, 1898, the physical property, rights, and franchises of Union Pacific Railway were sold to Union Pacific Railroad, signifying a significant transition within the company's structure and operations.

In 1899, Union Pacific gained control of OSL.

In 1901, Union Pacific acquired 38% of Southern Pacific stock, gaining control of the railroad.

The Western Pacific Railway was established in 1903 to construct the San Francisco to Salt Lake City route as a competitor to Southern Pacific.

The Los Angeles Limited was a passenger train service that operated in 1905. This train route provided transportation services to passengers traveling to and from Los Angeles during that period.

Construction of the Western Pacific Railway began in 1906 at Oakland, CA, as part of George Gould's Rio Grande-Missouri Pacific system.

In 1907, the Denver, Northwestern & Pacific Railroad finished its initial line west of Denver towards Bond, CO, planned as competition for the Denver & Rio Grande Western.

Union Pacific and Southern Pacific began using articulated steam locomotives in 1909, featuring a 'hinged' frame for negotiating sharp curves.

In 1913, the U.S. Supreme Court mandated Union Pacific to divest its 46% share of Southern Pacific stock and relinquish control.

In 1921, Union Pacific gained control of LA&SL.

In 1922, the Union Pacific and Southern Pacific railroads were separated, leading to significant changes in the railway industry.

As of December 31, 1925, Union Pacific, along with other rail lines, operated over 9,800 route-miles and 15,000 track-miles. This marked a significant extent of rail coverage for the company during that period.

The 7000 Class Sports Models made their debut in 1926, showcasing new advancements in locomotive design and technology.

The 6.21 mile-long Moffat Tunnel was completed in Colorado in 1928, allowing Denver & Salt Lake to shorten its route.

The debut of the M-10000 Streamliner in 1934 revolutionized passenger train travel with its innovative design and speed capabilities.

In November 1935, UP leased OSL, OWRR&N, and LA&SL for operation, leading to the consolidation of all four railroads into the Union Pacific System on January 1, 1936.

On January 1, 1936, Union Pacific consolidated OSL, OWRR&N, LA&SL, and St. Joseph & Grand Island into a single-line operation known as the Union Pacific System.

UP 4014 is a 4-8-8-4 Big Boy class freight steam locomotive, delivered in 1941. It is the largest operational steam locomotive in the world and was withdrawn from revenue service in 1961.

During World War II, a Boeing B-17 Flying Fortress named Spirit of the Union Pacific was dedicated to recognize war bond contributions from Union Pacific employees. Unfortunately, the plane was shot down over Germany in 1943, leading to most of its crew being taken as prisoners of war.

UP 844, also known as No. 8444, is a 4-8-4 Northern type express passenger steam locomotive that was the last steam locomotive built for UP. It has been in continuous service since its delivery in 1944.

UP 949, 951, and 963B are a trio of streamlined General Motors Electro-Motive Division E9 passenger locomotives built in 1955. They have been upgraded to be more compatible with modern locomotives.

In 1959, the last steam locomotive made its journey from North Platte to Cheyenne.

In 1960, Union Pacific engaged in a battle for the merger with Rock Island.

On January 30, 1969, the Board of Directors of Union Pacific Railroad Company approved the creation of Union Pacific Corporation as a new holding company. The reorganization involved an exchange offer for the existing preferred and common stock of the railroad company.

On August 28, 1969, Union Pacific and Celanese Corporation announced an agreement in principle for the acquisition of Champlin Petroleum Company and Pontiac Refining Corp. This deal included oil subsidiaries with significant daily production and refining capacities.

On June 26, 1971, all non-railroad properties of the Union Pacific Railroad were transferred to Union Pacific Corporation.

The Interstate Commerce Commission (ICC) approved the merger between Union Pacific (UP) and Chicago, Rock Island and Pacific Railroad (CRI&P) on November 8, 1974, after a lengthy and complex case.

Union Pacific withdrew its application to merge with Chicago, Rock Island and Pacific Railroad due to financial issues and ICC conditions. This led to the dismissal of the proposed merger.

UP 3206, a 4-6-2 type locomotive, was initially displayed at Highbridge Park in Spokane, Washington before being moved to the Spokane Interstate Fairgrounds in 1978.

On January 8, 1980, UP announced its intended merger with Missouri Pacific Railroad and Western Pacific Railway.

On September 13, 1982, UP was given ICC approval to control Missouri Pacific Railroad and Western Pacific Railway.

On October 20, 1982, the ICC approved UP's control and merger of Missouri Pacific and Western Pacific.

On January 1, 1983, Union Pacific officially took over the accounts and interests of Western Pacific and Missouri Pacific, solidifying its control over the two railroads.

In 1984, the merger between Union Pacific, Missouri Pacific, and Western Pacific railroads was approved, leading to the consolidation of these major railway companies.

On January 1, 1986, Union Pacific and Missouri Pacific merged their operating departments into a single organization. UP also started applying Union Pacific lettering on repainted MP locomotives instead of Missouri Pacific lettering.

On November 14, 1986, Union Pacific and MKT filed their intention to merge with the Interstate Commerce Commission (ICC). This marked a significant step towards the potential merger of the two railroads.

On May 3, 1987, the Union Pacific Corporation merged its subsidiaries, Champlin Petroleum and the Rocky Mountain Energy Company, into a single group known as the Union Pacific Resources Group. This move aimed to enhance cost efficiency and productivity in the natural resource sector.

Western Pacific Railroad was formally merged into Union Pacific on June 17, 1987. This consolidation of railroads expanded Union Pacific's network and operations.

Oregon-Washington Railway & Navigation Co., Des Chutes Railroad, and Yakima Valley Transportation Co. were merged into OSL on December 29, 1987.

Oregon Short Line Railroad was merged into Union Pacific on December 30, 1987.

Los Angeles & Salt Lake Railroad, Spokane International Railroad, and Mount Hood Railway were merged into Union Pacific on December 31, 1987.

On May 16, 1988, ICC approved Union Pacific's control of MKT.

On August 12, 1988, Union Pacific's control of MKT took effect.

Missouri-Kansas-Texas was merged into the Missouri Pacific on December 1, 1989, which was itself part of Union Pacific. Missouri Pacific was formally merged into Union Pacific on January 1, 1997.

In 1990, Union Pacific exchanged its 23 percent ownership of Los Angeles Union Passenger Terminal with Santa Fe Pacific Realty in exchange for property previously owned by LAUPT.

Union Pacific and Missouri Pacific announced the repainting of all Missouri Pacific locomotives into UP's yellow and gray scheme with Missouri Pacific lettering. The last MP-lettered yellow unit to be relettered to UP was ex MP MP15DC 1382.

The last MP blue unit, ex MP GP38-2 2103, was repainted and relettered to UP yellow. This was part of the process of repainting Missouri Pacific locomotives into Union Pacific's yellow and gray scheme.

On October 5, 1994, Union Pacific made an offer to buy and merge with Santa Fe Pacific Corporation for $3.4 billion, competing with BN's $2.5 billion offer.

On October 31, 1994, Union Pacific Corporation announced the sale of its USPCI subsidiary to Laidlaw, Inc. for a reported sum of $225 million. This divestiture marked a strategic decision in Union Pacific's corporate restructuring.

On February 21, 1995, the ICC approved Union Pacific's purchase of Chicago and North Western Railway (C&NW) under ICC Financial Docket 32133.

Union Pacific Corporation acquired 71.6 percent of Chicago & Northwestern Transportation Company stock, resulting in ownership of 99.5 percent of all CNWT stock.

Union Pacific's board of directors gave the green light to the merger agreement with Southern Pacific Railroad.

Union Pacific and Southern Pacific officially announced their merger agreement, marking a significant step towards consolidation.

UP formally merged with Chicago & Northwestern Transportation Company on October 1, 1995. This merger led to the cessation of C&NW's existence and compensation for its employees.

On January 17, 1996, Union Pacific's acquisition of Southern Pacific Rail Corporation was approved at a special meeting by 85 percent of SP's outstanding shares.

On August 6, 1996, Union Pacific's control of Southern Pacific, including D&RGW and SSW, was approved by the Surface Transportation Board (STB).

On September 10, 1996, the Union Pacific Merger Company was merged into the Union Pacific Corporation.

On September 11, 1996, Union Pacific Corporation was granted control of Southern Pacific Rail Corporation, which controlled various railway companies, with an effective date of October 1, 1996.

On October 15, 1996, Union Pacific Corporation spun off its remaining 83 percent stake in Union Pacific Resources Group, which owned 7.5 million acres of land in the western states.

Missouri Pacific Railroad was officially merged with Union Pacific Railroad, further consolidating the operations and influence of Union Pacific in the railroad industry.

The formal merger of D&RGW with Union Pacific Railroad took place, leading to a significant expansion of Union Pacific's network and resources.

In 1998, the Union Pacific Corporation merged the third Union Pacific Railroad into the Southern Pacific Transportation Company, which became the surviving railroad and was renamed as the fourth incarnation of the Union Pacific Railroad.

Union Pacific Corporation announced plans to relocate its corporate headquarters to Omaha by July 1, 1999. Negotiations began for the construction of a new headquarters building after the move.

In April 2000, Anadarko Petroleum Corp acquired Union Pacific Resources Group, a subsidiary of Union Pacific Corporation.

Following the terrorist attacks in New York City and against the Pentagon in Arlington, Va., Union Pacific tightened security across its system in 2001. The company also began adding large American flag decals to the sides of its locomotives.

In 2002, Union Pacific (UP) trains were utilized to transport the Olympic Flame to the Winter Games.

In January 2003, James R. Young became the Chief Executive Officer of Union Pacific.

The new Union Pacific headquarters building in Omaha was opened in June 2004, three years after the commencement of construction.

On May 16, 2005, Overnite, a company under Union Pacific Corporation, was sold to UPS.

In 2007, Jim Young was elected chairman of the board of Union Pacific. The company also unveiled the first of sixty new environmentally friendly ultra-low emission diesel locomotives for use in Los Angeles Basin rail yards.

In 2008, the Union Pacific opened its new headquarters in Omaha, Nebraska.

In 2009, a mudslide caused a disruption by severing the Cascade Line.

Maury Klein's 'Union Pacific: The Reconfiguration' is the third volume in his history of Union Pacific, published in 2011. It covers a period of UP's history, focusing on the personalities of the leaders of both the corporation and the railroad.

In March 2012, John J. Koraleski assumed the role of President at Union Pacific.

In 2013, Union Pacific reacquired the 'Big Boy' No. 4014 steam locomotive.

In February 2014, Lance M. Fritz took over as the Chief Executive Officer of Union Pacific.

In 2015, UP 844 was rebuilt and returned to service in 2016. It is notable for being the only steam locomotive to never be officially retired from a North American Class I railroad.

In the fiscal year 2017, Union Pacific reported earnings of US$3.388 billion and an annual revenue of US$24.46 billion, showing a 6.5% increase from the previous fiscal cycle. The company's shares traded at over $31 per share, with a market capitalization of US$105.2 billion in October 2018.

Restoration of UP 4014 to full operating condition was completed in May 2019, with its first excursion taking place that month. The locomotive was moved from Pomona to Cheyenne for restoration.

Union Pacific Corporation reported Total CO2e emissions (Direct + Indirect) for the twelve months ending 31 December 2020 at 9,157 Kt, which was a decrease of 1,258 Kt or 12.1% year-over-year. The company aims to achieve net zero emissions by 2050.

In 2021, Big Boy No. 4014 embarked on a ten-state steam tour covering 4,000 miles over 34 days.

Union Pacific provides an emergency contact number for customers, employees, suppliers, investors, and media to reach out in case of emergencies.

In August 2023, V. Jim Vena assumed the position of Chief Executive Officer at Union Pacific.