All I've found here are census data and the SSDI listing:
- 1920 Census, Rockford Ward 4, Winnebago Co., IL, #349/361, Jan. 16 & 17, 1920, Samuel Chamberlain, head, married, age unknown, NY/U.S./Illegible; ????, wife, age unknown, NY?/ U.S./illegible; George, son, age unknown, U.S./U.S./U.S.; living in residence headed by Maria Grow, a widow
- 1930 Census, Rockford Twp., Winnebago Co., Illinois, 25 Apr 1930, 215 Carborough? Ave., #331/397, Sam B?Chamberlain, head, $2250, age 37, married age 24, truck driver, WI/WI/WI; Olive E., wife, age 34, married, age 21, WI/WI/IL; George N., son, age 11, WI/WI/WI. Living next door is Alfred E? Cherry, age 53? & family, also from Wisconsin who might be related somehow
- SSDI lists George Chamberlain, b. 7 Jul 1918, d. Apr 1976, SSN #360-03-2624, issued IL
So, what you do know, in addition to his exact date and State of death (so you can obtain his death record which would list the informant for the death certificate, almost certainly a relative), is that your half-brother was the son of Olive E., b. c1896, WI, who died sometime after 1930, perhaps in Rockford, IL. Perhaps you already know whether she died before her husband's second marriage to Katherine Rose Webster (your mother), 27 May 1843, Rockford, IL, or whether there was a divorce and she died later on sometime. If you could find her obituary, it might mention son George Nelson's whereabouts at the time (I presume he was in the Military in 1943), and whether he was married at the time. Rockford, IL city directories and old phone books should tell you whether he lived there after WWII. Then, when his father died, 7 Jan 1966 in Rockford, there should be an obituary for him which would most likely mention his son, who was alive at the time. George would have graduated from high school there in Rockford in 1936 or 1937, so you could go there and try to track down some of his classmates who might know what became of him. I've used this system successfully in the past, beginning with obtaining a list of the graduates of his class from the high school or the local newspaper, then trying to find some of them who might still live there (of course most of them would be dead by now). It would be a long shot in this case. There are other places to look for information, I suppose, but these are the first ones that come to mind, in addition to Candis' suggestions. But, hopefully, your posting might elicit a response from someone who knew him. Do make sure to place a similar posting in GenForum, if you've not already done so.