As America expanded, and grew in both size and population, the principle record-producing jurisdictions, the U.S. counties, also grew in population, making the adjustment to smaller counties necessary. Changes in the boundaries were the norm, and not the exception for many years. Today the boundaries have pretty-well stabilized, but this wasn’t the case for many states up until about 1920. It was possible for a family to live in one place, never moving as much as 20 feet, but that family could well have lived in three, four, and maybe five or more counties. I remember hearing a story years ago about one family who lived in Oregon, never moving, but living in seven different counties. Now that’s an extreme example, but it proves the point that when doing genealogy research, we must often search the records of a number of counties to locate those of our ancestors. All the Federal Census records (1790-1930) and many state censuses are now online, and using name searches alone, we’re often able to find family members in a matter of minutes. Now and then we find these folks living in counties that may have been adjacent to, or nearby the county where we had expected to locate them. This is often due to nothing more than changes in the county boundaries.
By knowing what counties our ancestors lived in, we know where to look for not only those online census records, but all kinds of other records that 
may not be online. There are many records that we still can only access by searching through microfilm from the Family History Library, an archives, or the county courthouse itself.
Thorndale and Dollarhide produced a series of 50 maps showing the county boundary changes as they were on the Federal decennial census years – 1790 through 1920. The maps were produced over a period of years and sold in Map Guide Packets. Eventually the maps were compiled into the best-selling Genealogy volume, Map guide to the U.S. Censuses 1790-1920.
DOLLARHIDE MAP GUIDE PACKETS
Alabama http://www.familyrootspublishing.com/store/product_view.php?id=300
Alaska http://www.familyrootspublishing.com/store/product_view.php?id=301
Arizona http://www.familyrootspublishing.com/store/product_view.php?id=302
Arkansas http://www.familyrootspublishing.com/store/product_view.php?id=303
California http://www.familyrootspublishing.com/store/product_view.php?id=304
Colorado http://www.familyrootspublishing.com/store/product_view.php?id=309
Connecticut, Massachusetts, Rhode Island http://www.familyrootspublishing.com/store/product_view.php?id=390
Florida http://www.familyrootspublishing.com/store/product_view.php?id=316
Georgia http://www.familyrootspublishing.com/store/product_view.php?id=373
Hawaii http://www.familyrootspublishing.com/store/product_view.php?id=317
Idaho http://www.familyrootspublishing.com/store/product_view.php?id=319
Illinois http://www.familyrootspublishing.com/store/product_view.php?id=321
Indiana http://www.familyrootspublishing.com/store/product_view.php?id=323
Iowa http://www.familyrootspublishing.com/store/product_view.php?id=325
Kansas http://www.familyrootspublishing.com/store/product_view.php?id=327
Kentucky http://www.familyrootspublishing.com/store/product_view.php?id=375
Louisiana http://www.familyrootspublishing.com/store/product_view.php?id=329
Maine http://www.familyrootspublishing.com/store/product_view.php?id=331
Maryland, Delaware, District of Columbia http://www.familyrootspublishing.com/store/product_view.php?id=333
Michigan http://www.familyrootspublishing.com/store/product_view.php?id=394
Minnesota http://www.familyrootspublishing.com/store/product_view.php?id=335
Mississippi http://www.familyrootspublishing.com/store/product_view.php?id=337
Missouri http://www.familyrootspublishing.com/store/product_view.php?id=339
Montana http://www.familyrootspublishing.com/store/product_view.php?id=341
Nebraska http://www.familyrootspublishing.com/store/product_view.php?id=343
Nevada http://www.familyrootspublishing.com/store/product_view.php?id=345
New Hampshire, Vermont http://www.familyrootspublishing.com/store/product_view.php?id=347
New Jersey http://www.familyrootspublishing.com/store/product_view.php?id=349
New Mexico http://www.familyrootspublishing.com/store/product_view.php?id=351
New York http://www.familyrootspublishing.com/store/product_view.php?id=377
North Carolina http://www.familyrootspublishing.com/store/product_view.php?id=353
North Dakota http://www.familyrootspublishing.com/store/product_view.php?id=355
Ohio http://www.familyrootspublishing.com/store/product_view.php?id=379
Oklahoma http://www.familyrootspublishing.com/store/product_view.php?id=392
Oregon http://www.familyrootspublishing.com/store/product_view.php?id=357
Pennsylvania http://www.familyrootspublishing.com/store/product_view.php?id=381
South Carolina http://www.familyrootspublishing.com/store/product_view.php?id=359
South Dakota http://www.familyrootspublishing.com/store/product_view.php?id=361
Tennessee http://www.familyrootspublishing.com/store/product_view.php?id=383
Texas http://www.familyrootspublishing.com/store/product_view.php?id=363
Utah http://www.familyrootspublishing.com/store/product_view.php?id=365
Virginia http://www.familyrootspublishing.com/store/product_view.php?id=385
Washington http://www.familyrootspublishing.com/store/product_view.php?id=367
West Virginia http://www.familyrootspublishing.com/store/product_view.php?id=369
Wisconsin http://www.familyrootspublishing.com/store/product_view.php?id=387
Wyoming http://www.familyrootspublishing.com/store/product_view.php?id=371
