No expert here but I agree it’s from the 1800’s, and made in New England. Even if the house is from the 1700’s, installing a newer lock is not an uncommon practice. The lock case cover appears to be a cast iron piece and not blacksmith made. I don’t believe cast iron lock cases were made here during the 1700’s. Not allowing the lock to be opened and inspected because the house is a museum, is a little ridiculous. Given the circumstances, this should be done by a qualified locksmith. A lock is first, a small machine, not just some pretty metal attached to a door. If the lock breaks, will they just live with it? You might want to contact the Lock Museum in Terryville, Conn., as there you will find someone with more expertise on early U.S. residencial door locks. It’s very possible they have one just like it. Doug