A Guide to Civil War Research.
You will find particularly near state lines that many men joined units in other states. Don't forget to check the Naval Records if your man is not found elsewhere.
I found in my research that although my mother's family, the Hammonds, had gone to Dahlonega, Georgia for the gold rush in 1834 and settled in north Alabama, they returned to South Carolina and fought in a South Carolina unit.
You will also find a number of north Alabama men in with Virginia Cavalry units, Kentucky men with Tennessee Cavalry Units and East Tennessee and West Virginia men in with Virginia Units. Many thousands of men from Maryland and Pennsylvania joined Virginia Units and fought for the south. In Georgia some 10,000 men went to Mississippi and joined up with units there early in the war because Gov. Brown refused to let his troops join the Confederacy. Likewise many North Carolina men joined in surrounding states when the Governor tried to make them all "tarheels" and stay within the bounds of North Carolina.
Although Andrew Booth did a great job of compiling service records for Louisiana troops, his compilation contains about 80,000 names and the total who served from Louisiana were about 142,000 - thus fully 40% of the men either served in other states' units or are otherwise undocumented in the compiled service records. While we can't generalize that number for the other states, nonetheless many of the men who served from each state are not easily found in the existing records.
This set of OnLine lessons is excerpted from our "Guide to Civil War Research" books. We have specific volumes for some states and a general volume which will help you research other states.