 Prior to the United States ' Civil War , Catholicism grew slowly in America , but afterward , it became more widespread as Catholic immigrants from eastern Europe moved to the four counties , which include Armstrong , Fayette , Indiana , and Westmoreland , to mine coal and produce coke to fire steel mills in Pittsburgh . This influx of Catholic immigrants resulted in the creation of more than 80 parishes and missions in the counties between 1865 and 1917 . 
