Preston is a town in Caroline County, Maryland, United States. The population was 566 at the 2000 census. The ZIP code is 21655. The primary phone exchange is 673 and the area code is 410. Preston is home to the Linchester Mill, circa 1682. During the Revolutionary War it supplied grain to George Washington's troops. It was listed on the National Register of Historic Places in 2009 along with the Jacob and Hannah Leverton House.