Erected by Pope John Paul II on 25 March 1992 by the bull Totus Tuus Poloniae populus. It corresponds to the territory of an earlier Diocese of Chełmno, erected by Pope Innocent IV on 29 July 1243. The capital of the diocese is Pelplin with the Cathedral of the Assumption of the Blessed Virgin Mary. The patrons of the diocese are St. Lawrence, deacon and martyr, and St. Bernard, abbot and Doctor of the Church.