Horg is a former municipality in the old Sør-Trøndelag county, Norway. The 291-square-kilometre (112 sq mi) municipality existed from 1841 until its dissolution in 1964. The municipality of Horg encompassed the southern part of what is now the municipality of Melhus in Trøndelag county. The municipality included areas on both sides of the river Gaula. The administrative centre was the village of Lundamo. The main church for the municipality was Horg Church.