Manatee County is a county in the U.S. state of Florida. As of the 2020 US Census, the population was 399,710. Manatee County is part of the Bradenton-Sarasota-Venice, Florida Metropolitan Statistical Area. Its county seat and largest city is Bradenton. The county was created in 1855 and named for the Florida manatee, Florida's official marine mammal. Features of Manatee County include access to the southern part of the Tampa Bay estuary, the Sunshine Skyway Bridge, and the Manatee River.