Leoncin pronounced [lɛˈɔnt͡ɕin] is a village in Nowy Dwór County, Masovian Voivodeship, in east-central Poland.

It has a neogothic church from 1885, as well as a wooden chapel dating from the end of the 18th century that is located at a nearby cemetery.

[2] The Jewish community of Leoncin during the partitions of Poland was relatively small, totalling about 30 business families, some cultivating orchards, others running taverns or involved in manufacture.

In the following years, due in part to economic difficulties as well as Zionist agitation, many left in search of greener pastures.

[2] During the Holocaust in occupied Poland, in the winter of 1940–41 the remaining Jewish inhabitants of Leoncin were deported by German forces to a transit ghetto in Nowy Dwór Mazowiecki and from there to extermination camps.