The best source for local historical maps is usually your town historical society and your town library. Before the 1830s there was little perceived need for maps, but in the mid-1830s, the state mandated a general survey mapping of each town, and some of those maps are often available on the internet.
The National Heritage Museum's Library and Archives collection holds approximately 100 maps documenting the exploration and growth of North America as well as the development of the colonies. Among these holdings are a number of Revolutionary War battle maps, traveler's aids published during the period of westward migration, and maps that delineate roads, waterways, and mineral resources.
Maps are a great primary source teaching aid. There are several web sites that specialize both in providing old maps as primary sources and in teaching how to read and analyze maps in the classroom: Lewis & Clark: The Maps of Exploration 1507-1814, Special Collections Library, University of Virginia; Mapping Colonial New England, a lesson plan of EDSITEMENT, the education website of the National Endowment for the Humanities; History Matters, maps online feature links including the Library of Congress, Historic USGS Maps of New England, and cartography archives. There is also a special feature on “Making Sense of Maps” as primary source documents.