Casselberry is a city in Seminole County, Florida, United States. The population was 22,629 at the 2000 census. According to the U.S Census estimates of 2009, the city had a population of 24,792. It is usually considered a suburb in the OrlandoKissimmee-Sanford Metropolitan Statistical Area. Casselberry features over 30 lakes and ponds, the largest being Lake Howell, the Triplet Chain of Lakes, Lake Kathryn, and Lake Concord.