Sumter County is a county located in the U.S. state of South Carolina. As of the 2020 census, the population was 105,556. Its county seat is Sumter. Sumter County comprises the Sumter, SC Metropolitan Statistical Area, which is also included in the Columbia-Sumter-Orangeburg, SC Combined Statistical Area. The county is also part of "The Midlands" area. It is the home of Shaw AFB, headquarters to the 9th Air Force, AFCENT, United States Army Central, with a number of other tenant units.