St. Petersburg is a city in Pinellas County, Florida, United States. As of the 2015 census estimate, the population was 257,083, making it the fifth-most populous city in Florida and the largest in the state that is not a county seat (the city of Clearwater is the seat of Pinellas County). St. Petersburg is the second-largest city in the Tampa Bay Area, after Tampa. Together with Clearwater, these cities comprise the Tampa–St. Petersburg–Clearwater Metropolitan Statistical Area, the second-largest in Florida with a population of around 2.8 million. St. Petersburg is located on a peninsula between Tampa Bay and the Gulf of Mexico, and is connected to mainland Florida to the north. St. Petersburg was founded in 1888 by John C. Williams, who purchased the land, and by Peter Demens, who brought the railroad industry into the area.