Galveston County is a county in the U.S. state of Texas, located along the Gulf Coast adjacent to Galveston Bay. As of the 2020 census, its population was 350,682. The county was founded in 1838. The county seat is the City of Galveston, founded the following year, and located on Galveston Island. The most-populous municipality in the county is League City, a suburb of Houston at the northern end of the county, which surpassed Galveston in population during the early 2000s.