Gmina Leoncin is a rural gmina (administrative district) in Nowy Dwór County, Masovian Voivodeship, in east-central Poland. Its seat is the village of Leoncin, which lies approximately 12 kilometres (7 mi) south-west of Nowy Dwór Mazowiecki and 37 km (23 mi) north-west of Warsaw.
The gmina covers an area of , and as of 2006 its total population is 5,092 (5,435 in 2011).
Gmina Leoncin contains the villages and settlements of Cisowe, GaÃÂ, Gà Âusk, Gniewniewice Folwarczne, Górki, Krubiczew, Leoncin, Maà Âa Wieà  przy Drodze, Michaà Âów, Nowa Dàbrowa, Nowa Maà Âa Wieà Â, Nowe Budy, Nowe Gniewniewice, Nowe Grochale, Nowe Polesie, Nowiny, Nowy Secymin, Nowy Wilków, Oà Âniki, Rybitew, Secymin Polski, Secyminek, Stanisà Âawów, Stara Dàbrowa, Stare Gniewniewice, Stare Grochale, Stare Polesie, Teofile, Wilków nad Wisà ÂÃÂ, Wilków Polski, Wincentówek and Zamoà ÂÃÂ.
Gmina Leoncin is bordered by the gminas of Brochów, Czerwià Âsk nad Wisà ÂÃÂ, Czosnów, Kampinos, Leszno and Zakroczym.