Almost all the American chestnuts died long ago from a blight. If it turns out to be real chestnut, let some tree people know about it. I'm sure they would love to get some seeds from this apparently blight-resistant tree. Such logs show up now and then and account for the supply of wormy chestnut that still exists. The chestnut that I've sawn here in Western Washington has no blight, and the wood looks identical to the pictures I've seen in hardwood books.
Horse chestnuts have opposite branching and a compound leaf, which is palmate, with five leaflets.
American chestnut has a simple leaf which is highly serrate. Most live chestnuts in yards are Chinese chestnuts, which are blight resistant. That would be my guess as to species. The wood is lighter and softer than oak. It was heavily used in construction, furniture, and millwork before the blight.