Great horn, and the Red paint makes it special! Just guessing here, but the spout looks like that found on Lancaster factory horns; the butt plug is not the same , while the carry staples are of the Lancaster type. With the loose fitting plug, it is likely that while very old, this one is a replacement done at some time in the past. The horn is much more finely made than the plug, for example. If a Lancaster horn it would date to the 1840s, most likely. Could have come west with a Leman rifle.
Dick