I queried Family Search for a George Brooks with spouse Sophia and residence Whiteside, IL, and came up with a number of hits. Here's a link to the results page: http://bit.ly/15ofkK2
With luck, perhaps you can find a death record, which may give his exact birthplace or name his parents. At a minimum, it looks like he shows up in the 1870 and 1880 census. The best advice I can offer is to keep looking for more evidence and then to carefully parse it until you find another searchable lead.