The original wooden church, funded by the owners of Siedlątków, the Ubyszek family, was built in the 15th century. Around 1684, a new, single-nave brick church was built in its place. Fieldstone and brick were used as materials. It was later plastered.
The presbytery is rectangular in shape. The wider nave was originally two-bay. It was later extended westwards by one bay. Sections of the old façade have been preserved inside. In the presbytery, there is a barrel vault with modest stucco decoration at the seams. In the naves, there is a barrel vault with lunettes, and in the sacristy, a ceiling.
The main, Renaissance altar with the miraculous painting of Our Lady of Siedlątków burned down in 1957. The current one is a copy from 1958. The side, late Renaissance altar from the mid-17th century was enriched with painted scenes from the life of St. Isidore. The second, late Renaissance side altar is dated to the mid-17th century.
Other monuments of the church include: three processional crosses from the 18th century, a sculpture of St. John of Nepomuk, a Rococo monstrance from 1781, a chalice from the 17th century, a chalice from the beginning of the 17th century and chasubles from the turn of the 18th and 19th centuries.
In the 1970s, the church in Siedlątków was to be dismantled and moved to another location. All because of the construction of the largest artificial reservoir in central Poland, Jeziorsko. Ultimately, it was decided to leave it on the embanked headland.