Osieck [ˈɔɕɛt͡sk] is a town in Otwock County, Masovian Voivodeship, in east-central Poland.

[2] Osieck was granted town rights in 1558 by King Sigismund II Augustus.

King Sigismund III Vasa and the Royal Court stayed in Osieck during the epidemics of 1625, 1629 and 1630.

Osieck was deprived of its town rights by the Tsar on June 1, 1869, which was a way to punish the city for the participation of its inhabitants in the January Uprising.

Following the joint German-Soviet invasion of Poland, which started World War II in September 1939, the town was occupied by Germany.