The formerly independent municipalities of Bremgarten and Feldkirch belong to Hartheim. The municipalities, which were independent before the municipal reform in Baden-Württemberg in the 1970s, form the three districts of the municipality. The districts also form residential districts as defined by the Baden-Württemberg municipal code, and the two districts of Bremgarten and Feldkirch have been set up as localities, each with their own local council and local head as its chairman. The Bremgarten district includes the village of Bremgarten, the hamlet of Weinstetten and the residential area of Weinstetter Mühle. The north-eastern part of the Breisgau business park is also located in the Bremgarten district. The district of Feldkirch includes the village of Feldkirch and the district of Hartheim includes the village of Hartheim and the Rheinwärterhaus residential area.