Some close up pics/a few more may help but I'll give you the "first guess".
(if this is "original")
Based on the long foot of the forestock, the trigger guard and general butt shape/butt plate, I would suggest this is an Ohio built rifle which was typically produced in the 1840's/50's (although could be a little earlier).
The lock looks somewhat like a hardware store Goulcher lock that could have been produced by Eagle Gun Works (1844-1851), although many had "Goulcher" stamped/cast into the plate just forward of the screw fastening the hammer to the lock (but not always - and floral decorations on the lock were typical).
The side plate is the only thing that looks really "non-typical" for an Ohio of that period. It would be more at home on a rifle built a little further west (which is why I stated "if original" - because aside from that side plate, the rifle screams Ohio to me).