Casselberry is a city in Seminole County, Florida, United States. The city is part of the Orlando–Kissimmee–Sanford Metropolitan Statistical Area. Its population was 28,794 at the 2020 census.

Seminole County is a county located in the central portion of the U.S. state of Florida. As of the 2020 census, the population was 470,856, making it the 13th-most populated county in Florida. Its county seat and largest city is Sanford. Seminole County is part of the Orlando-Kissimmee-Sanford, Florida Metropolitan Statistical Area.