This week I took the Military Records III: Post Civil War Course the IGHR at Samford University in Birmingham, AL. I learned how to identify and trace units; a vital piece to understanding any soldier or sailor's service.
One of the best places to start your search is with the services historical centers. All have research guides and tons of information online.
The Army's is in Carlisle, PA and can be found online here.
The Navy's is at the Naval Yard in Washington, DC and can be found online here.
The Marine Corps is in Quantico, VA and online here.
The Air Force is in Montgomery, AL at Maxwell AFB. Details are here.