Complex sentence: The mid-portion of this border is interrupted by Washington, D.C., which sits on land originally part of Montgomery and Prince George's counties, including the town of Georgetown, Maryland, that was ceded to the Federal Government in 1790 to form the District of Columbia.
Split into simpler sentences: The mid-portion of this border is interrupted by Washington, D.C., which sits on land that was originally part of Montgomery and Prince George's counties and including the town of Georgetown, Maryland. This land was ceded to the United States Federal Government in 1790 to form the District of Columbia.