https://en.wikipedia.org/wiki/List_of_Catholic_dioceses_in_the_United_States

definition of a large town: any town in the UK that has a cathedral

 (= large, important church): 
1 b  An incorporated British town usually of a major size or importance having the status
of an “episcopal see” the place where the bishop is actually seated
there are 12 -24 bishops that cover various territories of the united states            
may be similar to district courts.       33 Districts in the US.