One of the very historical paces in Knyszyn is the church which may be one of the greatest tourist attractions. There are some evidence that the Roman-Catholic Parish had been existing at the begining of the 16th century. In 1520 a new church had been founded by a Lithuanian Chancellor, Mikołaj Radziwiłł. Some records from 1731 say that there were two churches in Knyszyn. One of them was made of briks and it was situated naer the corner of the centre of town. The other church was wooden and it was situated in the centre of Knyszyn.

The pressent, the oldest in Białystok Archidiocese, St. John the Evangelist Church, was fiunded by Jan Zamoyski. It is a brick church and an original wooden ceiling. The church made of bricks was consecrated on 21 March 1601 by Bishop of Vilnus, Benedykt Wojno. In 1710 the fire destroyed it, and in1722 the church was rebuilt according the instructions of Bishop Maciej Ancuta.
From the preseved books you can find out  that heart of king Zygmunt August has been stored underground of the church. Iside the church there is a plaque with the words of the king: "I am not king of your consciensce".