Use Ancestry to identify where an ancestor lived in 1860. That will help you place him in a military company raised in his home county. Without that background, it's just a guess, and based on a name/state match, many people guess wrong.
Don't use Ancestry for military records. That path leads far more people astray than otherwise.
If you find multiple families in the same county, it's likely to have more than one of them in the same company. However, you should be aware that for different reasons men often served in more than one command during the war. An ancestor's name could be associated with four or five different military units. Many researchers find one service record and stop with that, thinking it's the only one.
Since service record information is primarily narrative in nature, I don't find it useful to enter most of it into a true database. Since strong search capabilities exist for both the internet and most retail software, it's really not beneficial to sort and arrange ancestral data by military unit. That is, unless you simply want to do it.
Most people seem to expect service file matches for every male in their family. If a boy was out of diapers or a man not yet in his coffin, they are sure he served. Truth is that most parents were anxious to keep young boys out of the army, and older men were far more useful at home than they were in the military.
There are countless other reasons not to find a military record match for your ancestor. Not long ago, I spent hours of valuable time trying to find military records for two young men. There didn't seem to be any good reason for them not to have enrolled. After further review, I learned that these two had been born blind.
Didn't someone in a movie say that military records were like a box of chocolates?