Regiments were usually made up, at the beginning of the war, to local areas and usually involved only one or two counties in each State. As the war progressed and the need arose for more soldiers, the areas searched for replacements increased to several counties and,in most States, State-wide. So, to answer your question, yes - a man living in St Joseph County could have been enlisted in Evansville. Perhaps he was there on business when he decided to enlist.