County, even state, lines have changed, and you can waste lots of time hunting in various county records and come up empty-handed because of this. Your ancestors may not have moved, but rather the county or state boundaries did, and the records you need are elsewhere. Soon after one is bitten by the genealogy bug, a dozen questions arise regarding how to trace ancestors. But, to get answers one must learn how to ask the right questions, particularly of librarians who can only help if they understand your research problem. Even experienced genealogists falter occasionally when faced with determining what it is they really want to know in order to make a research goal.
Genealogical research is accomplished, one step at a time.
Write down everything you now KNOW about an ancestor. If not, start doing so. Analyzing what you know at various stages of your research will enable you see at a glance what do not know. Then you can focus on determining what records exist that might answer your questions and where and how those records can be accessed. The amount of sources is enormous.