I don't knowanything about your Grandfather, but I think his wife Minnie will tie to some of my lines.
Go to the Illinois marriage datebase(http://cyberdriveillinois.com/cgi-bin/archives/marriage.sFill in just Mustard for the Grooms name and it will bring up all the Mustard marriages in the state of Ill for 1763-1900.
There is a George Mustard who married Minnie Haggy onFeb 7, 1985 in Fulton County.There are a lot of other Mustard's from Fulton County, so you may get a lot of information from this page.
I am distantly related to Minnie Haggy.Her family is from Cumberland County Ill.I don't remember who her parents are, but will look it up tonight when I get home.
I know I have a couple of pictures of ______ Mustard at home in an old photo album.She is probably a child of Minnie and George.Have any of your great-aunts ever talked about relatives in Minnesota by the name of Canny?Thats the family that had these photo albums.You can e-mail me directly at: email@example.com