St. Petersburg is a city in Pinellas County, Florida, United States. As of the 2020 census, the population was 258,308, making it the fifth-most populous city in Florida and the most populous city in the state that is not a county seat. It is the second-most populous city in the Tampa Bay area, which is the second-largest metropolitan area in Florida with an estimated population of about 3.29 million in 2022.