"Census Regions and Division of the United States" by US Census Bureau. Licensed under Public Domain via Wikimedia Commons.
These collections of primary sources are divided by regions defined by the Census Bureau.
New England
Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont
Mid-Atlantic
New Jersey, New York, and Pennsylvania
East North Central Midwest
Illinois, Indiana, Michigan, Ohio, and Wisconsin
West North Central Midwest
Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota
South Atlantic
Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington D.C., and West Virginia
East South Central
Alabama, Kentucky, Mississippi, and Tennessee
West South Central
Arkansas, Louisiana, Oklahoma, and Texas
Mountain
Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, and Wyoming
Pacific
Alaska, California, Hawaii, Oregon, and Washington