Slag
wow is that rare, that is one of the oldest Illinois I know of .. how wonderful you still have it and treasure it.   The Illinois watches throughout their history were one of the the top models produced anywhere. They are highly prized by collectors and from what my repair guys say, one of the best to work on ... great watch thanks for sharing. I have an Illinois that dates to the early 1900's I believe. Wonderful time keepers also. Here is some history of the company

Illinois watch company