Pope Pius VII erected the Diocese of Podlasie on 30 June 1818. It was abolished by the tsarist authorities in 1867. On 24 September 1918, it was reactivated by Pope Benedict XV and renamed Diocese of Siedlce on 28 October 1925. The capital of the diocese is Siedlce with its Cathedral of the Immaculate Conception of the Blessed Virgin Mary. The main patrons of the diocese are Saints Apostles Simon and Juda Thaddeus.