Twin Falls County is a county in the south central part of the U.S. state of Idaho. As of the 2020 census, the population was 90,046, making it the fifth-most populous county in Idaho. The county seat and largest city is Twin Falls. Twin Falls County is part of the Twin Falls, ID Twin Falls Metropolitan Statistical Area.

Twin Falls is the county seat and largest city of Twin Falls County, Idaho, United States. The city had a population of 51,807 as of the 2020 census. In the Magic Valley region, Twin Falls is the largest city in a 100-mile (160 km) radius, and is the regional commercial center for south-central Idaho and northeastern Nevada. It is the principal city of the Twin Falls metropolitan statistical area, which officially includes the entirety of Twin Falls and Jerome Counties. The border town resort community of Jackpot, Nevada, 50 mi (80 km) south at the state line, is unofficially considered part of the greater Twin Falls area. Located on a broad plain at the south rim of the Snake River Canyon, Twin Falls, is where daredevil Evel Knievel attempted to jump across the canyon in 1974 on a steam-powered rocket. The jump site is northeast of central Twin Falls, midway between Shoshone Falls and the Perrine Bridge.