The 1900 Census of Oklahoma Territory covered Beaver, Blaine, Canadian, Cleveland, Custer, Day, Dewey, Garfield, Grant, Greer, Kay, Kingfisher, Lincoln, Logan, Noble, Oklahoma, Pawnee, Payne, Pottawatomie, Roger Mills, Washita, Woods, and Woodward Counties, plus the Lands of the Osage and Kaw; Otoe and Missouri; Ponca; Wichita, Kiowa, and Apache. Some of these Territorial Counties kept their names and boundaries after statehood; some kept their names but had different boundaries; some were reorganized with new names.

The 1900 Census of Indian Territory covered the Quapaw Tract and the Five Nations: Cherokee, Chickasaw, Choctaw, Creek, and Seminole. The Seminole Nation was undivided. The Cherokee and Creek Nations were divided into districts, the Chickasaw Nation into Counties, and the Choctaw Nation into Districts and Counties within each District. None of these territorial units survived intact into statehood.

Today's counties were created at or after statehood [1907].