I just tried to find George Charles Nelson in the 1860 and 1850 census without any luck. I wonder where he was hiding? Here are a couple of things I found on the Illinois State Archives web site.
Here's his civil war information:
Name NELSON, CHARLES G Rank PVTCompany DUnit10 IL US INF
Personal Characteristics Residence PHELEN, MADISON CO, ILAge 24Height 5' 8Hair BLACK Eyes BLUEComplexion DARKMarital Status N/AOccupation FARMER Nativity KY
Service Record Joined When FEB 23, 1864Joined Where ALTON, IL Joined By Whom CPT ABBOTTPeriod 3 YRS Muster In FEB 23, 1864Muster In Where ALTON, IL Muster In By Whom N/AMuster Out MAY 30, 1865 Muster Out Where SPRINGFIELD, ILMuster Out By Whom CPT HALL Remarks PRISONER OF WAR MO UNDER TELEGRAM FROM WAR DEPT OF 12 MAY 1865
And here's George and Margaret's marriage date:
NELSON, GEORGE CmarriedROWDEN, MARGARET E 08/31/1865Bk 2/page 180CALHOUNCOUNTY
I also found where George C. Nelson homesteaded some land in Maries Co, MO in 1875. You might also want to look into ordering his homestead packet from the National Archives. The information on his homestead is from the BLM web site: