The article discusses the history of the Catholic Church in Irkutsk between the 1820s and the 1850s as well as the attitude of the Siberian authorities to the erection of the church. On the basis of birth certificates the number of people of Catholic faith in Irkutsk has been determined. The article presents accounts of eyewitnesses - political exiles and the inhabitants of the city - of priests, masses and religious festivities. A lot of attention has been devoted to the role of the Catholic Church and its great importance in the lives of the political exiles and the emerging Polish community