Largo is the third largest city in Pinellas County, Florida, United States, as well as the fourth largest in the Tampa Bay area. As of the 2020 Cen…Largo is the third largest city in Pinellas County, Florida, United States, as well as the fourth largest in the Tampa Bay area. As of the 2020 Census, the city had a population of 82,485, up from 77,648 in 2010.