Gainesville is the county seat of Alachua County, Florida, United States, and the most populous city in North Central Florida, with a populatio…Gainesville is the county seat of Alachua County, Florida, United States, and the most populous city in North Central Florida, with a population of 145,212 in 2022. It is the principal city of the Gainesville metropolitan area with a population of 350,903 in 2022.