County history books are usually excellent genealogical resources. They were very popular in the 1880’s and 1890’s, particularly with northern counties, though a few counties in the south printed them, as well. They actually did have a lot of useful information on county history in them, often from the times before American settlement, and were useful as school books for students who were studying local history. Most had a section for biographies for prominent or wealthy local citizens, as well. This is where their genealogical usefulness really comes in.
First of all, the people who are profiled in these county history books usually paid to be included. This meant that they had the money necessary to pay to get into these books. If your ancestor or a collateral relative is included in a county history book, that alone tells you that they had enough money to pay their way into the book. These books were often handed down through families, because they were vanity books. The person who paid to be included were proud of their inclusion, and would show the books to their family and friends with pleasure and delight. They were so proud of their inclusion that they handed the books down to their heirs, and the books sometimes became family heirlooms, at least for as long as anyone in the family was alive who personally remembered the person who was profiled in it.
The people who were profiled in these books submitted their own biographies and sometimes pictures to be included. Most of the time, you can trust the genealogical information they provided. You can learn a lot about your family history through the things they wrote and submitted to the books. There may be things in there you didn’t know about that branch of your family. You have to check out everything they said for accuracy, though, because it was not unheard of for someone to brag about an illustrious ancestry or outstanding achievements of their ancestors that were not true. They just wanted to make themselves sound more illustrious and important by making up outlandish, almost noble ancestries for themselves. This is not the norm, but it did happen, which is why you must check the biographies in county histories for accuracy.
You can also find out a lot of very real, very useful information about how your early ancestors lived in the county being profiled by reading the actual history part of these books. Sometimes, your ancestors may even be mentioned in the history sections if they did something instrumental in the founding of the county or its settlement, even without them having to submit a biography or be mentioned by a descendant who did.
You can often find these old county history books in local public libraries and historical societies today, unless you still have one that was handed down as a family heirloom in your family. If the book is in a library, it will usually be in a genealogy or history section of the library. You can also sometimes buy the books on eBay or find scanned versions of them that are readable online on Ancestry.com, which has a large collection of them.