Bridgett,
Here is how I did it for Saline County...it takes lots of time and patience but it is the only way to get as accurate of a count as possible. If every county in 1860 was done this way we would have a very accurate count (minus a small number) of just how many men served during the war.
I took the manuscript census of Saline County for 1860. It included area of what would become Grant Co later so these men were included for Saline Co. I did not include men who lived in what was Hot Spring Co in 1860 but later was Saline Co. They should be counted with Hot Spring Co.
ANyway,
1. I listed all males aged 10-65. This would allow for a few old men who got caught up and enlisted in 1861 as well as those youngsters who enlisted later (like my G Grandpa who enlisted at 14 in 1863-64).
2. I took these names and went name by name with the Compiled Service Records for Arkansas Confederate Soldiers and then for Arkansas Union Soldiers. It helps knowing what units formed in the county as that really helped with quick identification, especially with very common names like John Smith. The others, who enlisted in non Saline Co companies I had to go back and double check. With Fold3 on computer this is much easier, I had to use the old microfilm reels. I also checked numerous websites like the Edward Gerdes Ark in the Civil War site, the National Park Service Soldier search and any others I might run across. Some men served in more than one CS unit and may have served in both CS and US so you have to go through and eliminate these duplicates.
3. Since there may be men who do not have CSR cards, I then went through the Arkansas Pension Records for Saline, Grant, Pulaski, Hot Spring and Garland Counties. This identified quite a few who did not have CSR's or military records.
4. I found any wartime letters of men from the county and double checked all those men who they mentioned. I also checked Goodspeed's History for Saline County, as well as the mass index for all of the Saline's, the publication of our local history society. There are also militia officers listed for 1860-62 for all counties in the Kie Oldham collection at Ark History Commission. I counted these men as veterans as well since they served at various times.
After all of these I had a pretty good idea of who served at any point.
What I found was quite interesting. The greatly embellished stories that were passed down on Saline Co history I found to not be accurate. I suspect many counties are the same way. The old story from Goodspeed history was constantly passed down to the point someone actually tried to state it on a recent Ark Civ War Heritage Marker on the courthouse square until I was able to prove it wrong. That story was that over 1300 men served and less than 20% survived. What I found was that right at 1200 served and only 22% (264) who did not return. I found about 76% either on surrender rolls, or in subsequent censuses or other documents, like cemetery records, pensions etc. There were about 2% I couldn't determine what happened to them.
In the end out of a total population of a little over 6000 people there were just over 2100 Saline men between ages of 10-65 so about 57% served. If you just go with the military age males 18-35 or 17-45 a higher percentage served which is where all the inflation comes from. There were around 900 who did not serve with most being on the younger or older end but there were military age males none the less who served no side.
So with all that said, it would be interesting if every Arkansas county that existed in 1860 had this done, we would get a very good look at how many served during the war.
Sorry for long winded reply but this is one way to determine numbers.