Here are links to digitized county histories for all 50 states. Remember, there are many other county histories available, but are still under copyright. Look for those volumes on library shelves!
Note that those on FamilySearch might direct you to log in to your account, but you can be sure that the book is found in its collection.
Tools for Working with Maps & Land Records:
DeedMapper – Have you ever tried to make heads or tails out of the old “metes and bounds” property surveys? DirectLine Software sells DeedMapper, which will actually plot out the shape of a piece of property as described in the deed. I used this program a number of years ago to solve my Miller problem in Virginia. Since then, the newer version includes the ability to integrate it into GoogleEarth.
United States Map Resources:
Atlas of Historical County Boundaries
Atlas of the Historical Geography of the United States – This atlas, published in 1932, includes hundreds of clickable maps showing geographical changes through the years.
Bureau of Land Management Land Office Records – free, searchable database of land records beginning in 1820.
USGS Maps, Imagery and Publications
Sites with information on U.S. migratory roads and trails:
Cyndi’s List – Migration Routes, Roads and Trails
FamilySearch Wiki – U.S. Migration Trails and Roads
Sites that have large collections covering multiple, if not all, states:
Bureau of Land Management Land Patents
Historic USGS Maps of New England and New York at the University of New Hampshire
OldMapsOnline – This portal has links to historical maps around the world.
University of Texas, Perry-Castaneda Library Map Collection
USGS Historical Topographic Map Explorer
U.S. State Collections:
University of Alabama Historical Map Archive
Alaska Digital Archives
University of Connecticut
University of Delaware
University of Florida
University of Georgia
University of Idaho
Illinois – University of Chicago Library
Kansas – Wichita State University
Louisiana Digital Library
Maine – University of Southern Maine – Osher Map Library
University of Maryland
University of Michigan
Minnesota Digital Library
University of Nevada, Las Vegas
New Jersey – Princeton University
New Jersey – Rutgers University
New York Public Library
University of North Carolina
Oklahoma State University
University of Oregon
Pennsylvania – Free Library of Philadelphia
South Carolina – The South Caroliniana Library Map Collection
Tennessee State Library and Archives
Texas – University of Houston Libraries
Vermont – Middlebury College
Library of Virginia – including Civil War maps
University of Wisconsin Digital Collections
Canadian Map Resources:
In Search of Your Canadian Past: The Canadian County Atlas Digital Project
European Map Resources:
World Map Resources:
Brigham Young University Library – Maps, Atlases and Gazetteers: Maps and Atlases Online