O'Donnell was named for Tom J. O'Donnell, promoter of South Plains Railroads, including sixty miles of Santa Fe Line from Slaton to Lamesa. On this new railroad, important as a freight hauler, the town of O'Donnell was founded in 1909 by H. E. Baldridge and Charles H. Doak, two of the organizers and first officials of Lynn County. Doak built a hotel in the projected town in 1909, and L. G. Phillips established the first store. On July 4, 1910, a big picnic celebrated the arrival of the first Santa Fe train. The old Central post office, previously on Dee W. Harris Ranch, 5.5 miles northwest, was moved to the new town in 1910 and was officially renamed O'Donnell on Feb. 7, 1911. W. R. Standefer surveyed the townsite in 1911, and H. E. Baldridge offered free building lots to churches. A Methodist church was organized in 1911, Church of Christ and Presbyterian churches in 1912, and First Baptist in 1914. The town was incorporated in 1923, with W. R. Sanderson as first mayor. Its school, greatly improved from its early wooden building, serves a large area, and actor Dan Blocker, known as Hoss Cartwright, was a graduate. By 1961 O'Donnell was a dry land farming center and had what was then the largest cotton gin in the world, ginning 21,000 bales of cotton that year.