Located to the northwest of Washington, D.C. is the town of Leesburg, Virginia. The area is growing rapidly - there was a 40% increase in the population from 2000 to 2008 (to 40,000). Many working people are moving out from the city, while some retirees are doing the same. Crime is very low.
There is at least one very large planned community in Leesburg, Lansdowne. It has an active adult community within it (See Active Adult Community link at top right). Photo of Victorian mansion courtesy of and per license of Wikipedia and JoSePh.