callahan florida in what county
Sponsored Topics. Callahan is a town in Nassau County, Florida, United States, adjacent to Downtown Jacksonville. The population was 962 at the 2000 census. Callahan is located at 30Â°33â²39â³N 81Â°49â²51â³W / 30.56083Â°N 81.83083Â°W / 30.56083; -81.83083 (30.560702, -81.830850).