You have an interesting rifle with great stock architecture, despite being shortened. I think this is probably of southern origin, and being from the Midwest, it does not appear to be a Midwest rifle to me... too many nice details! Unfortunately, without barrel initials and the loss of original guard and replaced tang, i.d.-ing this gun becomes somewhat subjective. My thoughts on this rifle are the following:
The strongly triangular, crisp butt profile with substantial height and butt plate with small, raised ridge at end of it top extension, in addition to the use of small diamond inlays and a "different" patchbox symmetrical along its center line, all suggest a Carolina origin to me... perhaps more reminiscent of SC work than NC work... but that general area.
These rifles usually have a rather tight side facing around the lock plate, which is present here... except for the slightly "heavy" area just above the nose of the lock plate.
I think the rifle had a significantly longer barrel originally, probably a 4-pipe gun, which was common on better Carolina rifles. The lock on this gun is questionable. The side facing width is not even all the way around the current lock plate... note it is wider above the lock plate and rather thin along its bottom edge. That usually indicates the original lock has been replaced with a slightly large/wider lock during the gun's working life. This rifle may have always been percussion, but assuming a southern gun [which it probably is], single lock bolt flintlocks became popular by the mid-1820s often using double-throat cocks that did not require a stock cut just above the top edge of the lock plate. These large, unengraved patchboxes most often occur in the late flint/early percussion era, so the gun could go either way.
Perhaps going through Michael Briggs' or Bill Ivey's books on North Carolina rifles would turn up a "somewhat similar" side plate and help locate the gun. But from what your good photographs show us, I believe you have a southern rifle, probably from the Carolinas, and I'd learn toward South Carolina on this one due to the "different style" patchbox... unless Michael can point us in a better direction.
Shelby Gallien