Collier County is a county located in the U.S. state of Florida. As of 2000, the population was 251,377. The U.S. Census Bureau 2007 estimate for the county is 315,839. Its county seat is Naples. Collier County is coextensive with the Naples-Marco Island, Florida Metropolitan Statistical Area, a metropolitan statistical area (MSA) designated by the Office of Management and Budget and used for statistical purposes by the Census Bureau and other agencies.