Tulsa County is located in the U.S. state of Oklahoma. As of the 2020 census, the population was 669,279, making it the second-most populous county in the state, behind only Oklahoma County. Its county seat and largest city is Tulsa, the second-largest city in the state. Founded at statehood, in 1907, it was named after the previously established city of Tulsa. Before statehood, the area was part of both the Creek Nation and the Cooweescoowee District of Cherokee Nation in Indian Territory.

Tulsa is the second-most-populous city in the state of Oklahoma, after Oklahoma City, and is the 47th-most-populous city in the United States. The population was 413,066 as of the 2020 census. It is the principal municipality of the Tulsa metropolitan area, a region with 1,034,123 residents. The city serves as the county seat of Tulsa County, the most densely populated county in Oklahoma, with urban development extending into Osage, Rogers and Wagoner counties.