What country? In the USA most were State National Guard Units that were Federalized to be sent overseas. So look at the State Archives or State Capitol they lived or were in serviced for, also the counties and cities may have erected memorials or made proclamations about their "local boys" who served.
If did not survive the war then they could have a tombstone that cites service if remains returned to US. If buried overseas here is where you should find the burial.
http://www.abmc.gov/USGenWeb.org has State websites that most have Military databases and County websites with Military databases.