Are you sure you’re looking in the right county for those records?

When doing genealogical or historical research, it’s helpful (if not essential) to know what counties to search for the timeframe you’re interested in.  And as we all know, boundaries shift over time.  So you may think you know what counties to search, but is there a chance you’re missing something?

Take a look at this example.  Let’s assume you’re looking for records for your homesteading ancestors who settled in the region between Albuquerque, Los Alamos, and Santa Fe, New Mexico.  This animation shows the boundaries by decade from 1850 to 1950.  Those county boundaries were anything but stable.  Take for example the community of Los Alamos; it was part of the following counties during that period:  Santa Fe, Rio Arriba, Bernalillo, and Los Alamos.

And this is not the exception, it’s the rule.  According to historical geography expert John H. Long, on average, a county’s boundaries shifted 4.5 times during its existence.  Especially during times of colonization and westward expansion, the boundaries on those frontier counties typically shifted much more than that, new counties were created, and old counties became defunct, and counties swapped parcels of land.

So if you haven’t found some records on your ancestors where you expected to, here are 5 quick steps to see if shifting boundaries may be the culprit, and which other counties you might need to look in for the records you seek:

1.  Go to the Historical County Boundary Maps interactive tool.

2.  Type in a PRESENT-day place in the Place box.  For example, type Los Alamos, NM.  You can even type a present day address, county, or road name too, such as Canyon Rd, Los Alamos, NM.  Remember, even if you know the county name or place name used to be something different, you must type the PRESENT-day address, county, road or place, not the historical name.

3.  Tab over to the Year box, type the year you believe your ancestors settled in the area, then click the Go! button or press the Enter key.  To be safe, even if you know your ancestors settled the area in the 1880s, you might want to type 1870 in the box.

4.  To quickly see if you need to be concerned about shifting boundaries for this location, here’s a shortcut:  click the arrow key on the right side of the Year box to scroll forward a decade at a time (you can also click the arrow key on the left side of the Year box to scroll backward a decade at a time).

5.  For any given year where you see a shift, just click the map at the location you’re searching to see a box pop up with the name of the county and a little history on the nature of the most-recent boundary change as of that year.

The above method will quickly help you see which other counties you might need to look in for the records you seek.  If you’re searching on some online services such as, now you know which other county names to type into the search box.  If you’re looking for records that may be held at the local county courthouse, archives, or genealogical society, now you know which counties you need call on to see if they know which repository holds the records for the timeframe in question.

Also, the same approach outlined above works on the Historical World Boundary Maps interactive tool to see country boundary changes over time.

Finally, here’s a bonus for those who read this entire post!

If you want to make your map larger, I have added a small + button in the upper right corner of the map window that enlarges the map.

Happy mapping!

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