The collegiate church of the Assumption of the Blessed Virgin Mary in Uniejów was established in the years 1342 – 1349 by Archbishop Jarosław Bogoria Skotnicki, on the site of an older building destroyed by the Teutonic Knights in the invasion of 1331. In the next century, its nave was enlarged, and perhaps in the 16th century a chapel of the Blessed Virgin Mary was erected, funded by the townspeople of Uniejów. Before 1635, from the foundation of M. Głuchowski, the chapel of St. John (now Holy Cross) was added, while in the years 1666-1668 the Uniejów custodian, priest Boleszczyński, founded the chapel of blessed Bogumił, where the hermit’s relics were buried. In 1649, the nave of the church was raised, and the vaults were also transformed. Another renovation took place in 1876, when the shape of most of the window openings was changed. In 1939, during the military operations, the collegiate church was seriously damaged. In the years 1945-1946 the church was rebuilt.
The church was situated in the center of Uniejów, on a fenced plot, located at the north-west corner of the market square. It was built in the Gothic style of bricks in the Flemish bond, as an aisleless structure with a separate, narrower chancel with a polygonal closure in the east. Initially a three-bay nave, in the 15th century was extended westwards by two additional bays. The walls of all elevations were reinforced with three-step buttresses, between which originally ogival windows were pierced. Inside, initially only the chancel was given a cross-rib vault.
Webpage zabytek.pl, Kościół parafialny pw. Wniebowzięcia NMP i św. Floriana Uniejów.