Tulsa County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 603,403, making it the second-most populous county in Oklahoma, 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.