 The settlement was first mentioned as "Magnum Oszec" in a 1312 deed, when the area around Bledzew was temporarily under the rule of the Ascanian margraves of Brandenburg in the west.From about 1320 until the Partitions of Poland in the late 18th century, Osiecko belonged to the Greater Polish Poznań Voivodeship.In 1360 it was a possession of the Cistercian abbey at Zemsko.