On March 24, 1849, William Davis, who owned 3,000 acres (12 km2) where McKinney now stands, donated 120 acres (0.49 km2) for the townsite. Ten years later, McKinney incorporated, and in 1913, the town adopted the commission form of government.
By 1970, McKinney was surpassed in size by Plano. McKinney experienced moderate population growth, from 15,193 in the 1970 census, to 21,283 in the 1990 census. Both the city and the county were named for Collin McKinney, signer of the Texas Declaration of Independence, and a congressman for the Red River district of the Republic of Texas. He was the author of a bill establishing counties in the northern part of the state.