Fremont County is a county located in the U.S. state of Idaho. As of the 2020 census the county had a population of 13,388. The county seat and largest city is St. Anthony. The county was established in 1893, and was named for the explorer John C. Frémont. Fremont County is part of the Rexburg, Idaho micropolitan area, which is also included in the Idaho Falls metropolitan area.