The Episcopal Diocese of Quincy was a diocese of the Episcopal Church in western Illinois from 1877 to 2013. The cathedral seat (home of the diocese) was originally in Quincy but was moved to St. Paul's Cathedral in Peoria in 1963. In order to avoid confusion with the Roman Catholic Diocese of Peoria, the diocese retained the name of the location of its original "home" city, Quincy, where its cathedral seat was St. John's.