The legislature of the provisional State of Deseret defined the county in an October 5, 1850 act, which also designated Farmington as the seat due to its location midway between boundaries at the Weber River on the north and the Jordan River on the south. It was named for Daniel C. Davis, a captain in the Mormon Battalion. The county boundaries were altered in 1852, in 1854, in 1855, and in 1862. In 1880 the county gained part of the islands and waters of Great Salt Lake that had previously been attached to Salt Lake County. The county boundary has remained unchanged since that time.