from Henry W. Thomas: History of the Doles-Cook brigade ; p.456
MUSTER ROLL OF STEWART INFANTRY, COMPANY I,
TWENTY-FIRST REGIMENT, GEORGIA VOLUNTEER INFANTRY, C. S. A.
STEWART COUNTY, GEORGIA.
MERCER, GREEN L.— Private, May 1, 1864. Wounded in battle.
and a couple of online links:
MERCER, Green L. 21st Georgia Inf., Co. I, 12/13/1840 - 06/20/1926, Penile Bapt. Ch. Cem., Dale Co., Alabama
http://files.usgwarchives.net/al/statewide/cemeteries/csa_mc.txt
Green Lee Mercer Nov. 13, 1840 - Jun. 20, 1925, Peniel Baptist Church Cemetery, Dale Co., Alabama
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GSln=Mercer&GSfn=Green&GSbyrel=in&GSdyrel=in&GSst=3&GScntry=4&GSob=n&GRid=9914751&df=all&