Hartselle is the second largest city in Morgan County , Alabama , about 10 miles ( 16 km ) south of Decatur , and is included in the Decatur Metropolitan Area , and the Huntsville-Decatur Combined Statistical Area . Hartselle is the second largest city in Morgan County , Alabama , United States , about 10 miles ( 16 km ) south of Decatur , and is included in the Decatur Metropolitan Area , and the Huntsville-Decatur Combined Statistical Area .