Stumbling across a reference to a genealogy, church, county or town history that mentions your family is exciting. However, one should use caution and verify the data with other sources -- primary ones, if extant. Many genealogies have been erroneously compiled because previous researchers relied exclusively upon material that they found in print.
Information found in genealogies, county, town and church histories varies greatly in depth and accuracy. One should always be careful about accepting anything and everything in print as 100 percent accurate. Errors abound in almost all such works. Genealogies are the most suspect, particularly when sources of the information are uncited (as so many are) or if cited, not done properly to enable one to determine that the actual marriage record was examined, for example. It also is difficult to weigh the credibility of the source -- was he or she an eyewitness to an event or merely re-telling stories he or she had heard?
Town, county and church histories are a mixed bag. Some are excellent, while many are of dubious worth. Since many of the county histories published about a century ago were by subscription, and there was no independent verification of any of the genealogical information, be careful about accepting them on face value. These are known as "mug books." Anyone with enough money to subscribe could submit material. As a result, it is mostly the affluent of the time and locality whose names appear in the books. And, quite naturally, the virtues of the subjects are extolled, and some are so flowery as to be laughable.
Local histories vary in reliability also, but for the most part are probably more accurate than the "mug books." It is always wise to check P. William Filby's American and British Genealogy and Heraldry and its 1982-1985 supplement to see if the book you have found is mentioned. In Filby's books you will find under each title a brief description of the book, along with such comments as "many errors and omissions," "use with care," "not definitive, but useful" or "standard work on the subject." These comments can guide you as to the general reliability of the publication.
County histories often consist of two sections. The first being a history of the county and arranged by towns or townships and the second part being biographical and containing profiles of usually the prominent founding fathers and families who lived there when the book was published. These books can be valuable because some of the information may have been obtained directly from local individuals, who may have had first-hand knowledge of the facts. However, often these books were compiled by interviews or from questionnaires and the data was not edited or verified independently. Add the possibility of errors creeping in from the time the notes were taken to the typesetting process, and it is easy to understand why information might be wrong. Genealogical information found therein should be checked with primary and/or good secondary sources. However, one may find some wonderfully detailed genealogies in these old local histories.
Many town and county histories were produced for the American centennial in 1876 or for the bicentennial (1976) celebrations. Some have been re-printed recently. Town histories often include information about the founding fathers, biographies of the local political leaders, doctors, ministers, and other professionals. In them also one may find lists of those who fought in the Revolutionary or Civil War, or names of early town or county officials such as the sheriffs, council members, and postmasters. Some New England town histories include early vital records as well as church, probate and land records.
Finding copies of local histories and old genealogies and can force you to hone your detective skills. Many of these are out of print and few libraries offer them on interlibrary loan. First check to see if the Family History Library has a copy on microfilm. Visit a Family History Center near you and examine the Family History Library Catalog (it's on both CD and microfiche) under subject or author to determine if the publication has been microfilmed. If it has, you can order it (for a small fee) from Salt Lake City. It will be sent to the Family History Center near you.
If you know that a particular genealogy exists, but can't find it at the Family History Library, see if your library has Genealogies in the Library of Congress -- a multi-volume set. Check these for your family histories. Then consult Complement to Genealogies in the Library of Congress. If the genealogy you want appears in the latter, it will tell you which libraries have a copy of it. You may then be able to borrow it on interlibrary loan.
If you find a reference to a genealogy and you would like to have a personal copy of it, see if UMI has it. If it does, then you will be able to obtain it on microfiche. It will be fairly expensive, but sometimes this is the only available source. Bell and Howell offers an outstanding collection of genealogies, local histories, church histories and some vital records.
Local histories and old genealogies can be invaluable and usually are worth the extra effort it takes to track them down.