At high noon on April 22, 1889 the Oklahoma Land Run kicked off, and 50,000 people raced into the Unassigned Lands in Oklahoma. By the end of the day, the once desolate prairie was a tent city of 10,000, with town lots staked off. By the second week, schools were opened and being taught by volunteers until the regular school districts could be established. Within a month, Oklahoma City had five banks and six newspapers. By 1907, Oklahoma City had surpassed Guthrie (the territorial capital) as the population center and commercial hub of the Oklahoma Territory. When Oklahoma was admitted to the Union, Oklahoma City was designated the new state's capital. The capitol building was built in 1919, but without a dome, due to steel rationing of World War I.

Oklahoma City went through an astonishing number of booms and busts during the 20th century. The discovery of oil in 1928 brought a sudden influx of wealth to the city. Oil wells soon sprung up everywhere in the city, even on the south lawn of the capitol building. The city was hit hard by the Depression, as rural migrants and unemployed workers flocked to the massive shanty town on the south bank of the North Canadian River. World War II (and the resultant industries) brought recovery to Oklahoma City and saw the establishment of nearby Tinker Air Force Base. However, the city once again began to decline in the 1960s and 1970s, as families fled from the downtown area to the suburbs. Attempts at urban renewal came to naught, as the city leaders demolished the aging theater district and the Biltmore Hotel, but ran out of funds before they could construct the proposed Galleria Mall.