Complex sentence: The Episcopal Diocese of Washington is the ecclesiastical territory or "diocese" of the Episcopal Bishop of Washington which is comprised of the United States District of Columbia and Maryland counties of Charles, St. Mary's, Prince George's and Montgomery.
Split into simpler sentences: The Episcopal Diocese of Washington is the ecclesiastical territory or "diocese" of the Episcopal Bishop of Washington in the United States. The territory comprises the District of Columbia and the Maryland counties of Charles, St. Mary's, Prince George's and Montgomery.