This Civil War record is most likely for this William as there was/is no Oakland Co, IL:
Name: William Collins ,
Residence: Oakland County, Illinois
Enlistment Date: 09 August 1862
Distinguished Service: DISTINGUISHED SERVICE
Side Served: Union
State Served: Illinois
Unit Numbers: 402 402
Service Record: Enlisted as a Musician on 09 August 1862
Enlisted in Company K, 79th Infantry Regiment Illinois on 28 August 1862.
Mustered out Company K, 79th Infantry Regiment Illinois on 12 June 1865 in Camp Butler, Springfield, IL
IN where the first two children were born. Apparently the couple moved there shortly after their marriage.
IL Bef 1879 They moved back before the birth of daughter Flossie.
6/19/1880 E Oakland Twp, Coles Co, IL. The census taker found William at age 38, a farmer, wife Amanda was 24, with one small son, Charles, 1. Louis Benedick, 48, farm hand, was also counted there.
6/15/1900 Same place. That year at census time William was 57, had been married 23 years to Amanda J, 45, with 5 children but only 3 still survived. In the house were Charles C, 21, William H, 13, and Flossie B, 11. William and both parents were born in OH.
4/28/1910 Still there. William listed in the census at 67, Mandy J at 55, and married 34 years. Three of their five children were still alive. William was still farming.