That's a strange one. Any marks on it? Another user here found a massive ball with a 2 on it that we were able to find a match for an oversized fishing weight. Literally a 2lb weight.
I looked it over with a magnifying glass. No marks on it what do ever. Just some pitting. Just for some reference my house is in northern Illinois and was built in the late 1800's it's one of the original 12 houses that settled here.