Hialeah, Florida. Hialeah ( /ˌhaɪəˈliːə/) is a city in Miami-Dade County, Florida, United States. As of the 2010 census, Hialeah has a population of 224,669. Hialeah is the sixth-largest city in the state. It is a principal city of the Miami metropolitan area, which was home to an estimated 6,012,331 people at the 2015 census.