The Parish of St. Stanislaus the Bishop and Martyr in Siennica, belonging to the Siennica Deanery in the Warsaw-Praga Diocese, has a long history dating back to the 16th century. It was established on April 3, 1528, after prior approval by the Poznań Chapter in 1515. Initially, the parish was part of the Poznań Diocese, and with the development of the Church's structure, it became part of the Garwolin Deanery in 1603. In 1957, the Siennica Deanery was created, and the parish became one of the main religious centers in the region. Currently, its parish priest is Fr. Jerzy Danecki, who has held this position since 2022. The parish administers three chapels: the Chapel of the Capuchin Sisters, the chapel in the senior home, and the cemetery chapel. From an architectural perspective, the parish stands out for its dynamic history of construction transformations, including the tragedy of a fire that destroyed one of the churches in 1939, leading to the merger of two parishes into one entity. It is worth noting that the Parish of St. Stanislaus BM is one of the largest in Mazovia, a result of both local religious traditions and social activities for the community. The parish includes faithful from many towns, such as Bestwiny, Drożdżówka, and Swoboda, highlighting its regional importance and the culture of the Catholic community, which brings together different generations and traditions. Siennica, with a history dating back to 1220, is not only a place of worship but also an important point in the local cultural identity. Interestingly, the parish, along with its affiliated chapels, has long been involved in charitable and social activities, contributing to the integration of local communities and the preservation of Catholic traditions in the region.