Tulsa County is a county 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 County is included in the Tulsa metropolitan statistical area. Tulsa County is notable for being the most densely populated county in the state. Tulsa County also ranks as having the highest income.