According to the following newspaper item, Clarksville's population "before the war" was 6,000. The same item also mentions an (alas, unnamed) Alabama regiment, and an unnamed Tennessee regiment; The article may be of general interest, however.

http://chroniclingamerica.loc.gov/lccn/sn84028820/1862-03-13/ed-1/seq-1/#date1=1861&index=0&rows=20&words=Buckner+Clarksville&searchType=basic&sequence=0&state=&date2=1862&proxtext=Buckner+Clarksville&y=15&x=16&dateFilterType=yearRange&page=1

From:
Holmes County Republican (Millersburg, Ohio) 13 Mar 1862