It depends on which Newtown, Pennsylvania, you are referring to...
According to census.gov, the 2007 ACS population estimate for Newtown borough, Pennsylvania, is 2,347.
The 2007 ACS population estimate for Newtown township, Bucks County, Pennsylvania, is 18,961.
The 2007 ACS population estimate for Newtown township, Delaware County, Pennsylvania, is 11,803.
The Census 2000 population for Newtown CDP, Pennsylvania, is 244.