Madarcos (Spanish: [maˈðaɾkos] ) is a municipality of the Community of Madrid, Spain. It has an area of 8.46 km with a population of 49 inhabitants and a density of 5.79 inhabitants / km it is the town with the lowest population in the Community of Madrid.

It borders the municipalities of the Sierra Horcajo north and northwest; Horcajuelo of the Sierra and the Rincon Prádena east; Puentes Viejas south, and Gandullas Piñuécar- west. At its end is the desert of La Nava, in the hamlet of the same name, to the southeast of the town, on the edge of the M-137 that connects Buitrago del Lozoya with Montejo de la Sierra, past the turning Madarcos.

41°02′51″N 3°34′56″W / 41.04750°N 3.58222°W / 41.04750; -3.58222