The 1880 Census is online free at www.familysearch.org
There is no Robert Granger born in 1877 in Illinois on the 1880 Census.There is a Herlbert R. Granger born in 1877 in Illinois, living in Athens, Menard Co. in 1880.Could this be your Robert??
There is a Robert Granger born in 1877 in Wisconsin, still in Wisconsin on the 1880 Census.That is the only Robert Granger born in 1877 on the 1880 Census.
If you think either are possibilities, check the website and run a search to view the census information.Click on Search For Ancestors, then on the left-hand side of the page that comes up click on Census.Select the 1880 U.S. Census, and enter the information.