this looks like a victorian period single cuff button. there would have been 2 of the things on the back (you can see where the other one broke off) and originally there would have a pair of these cuff buttons. the style looks like it could be 1870s-1890s and the metal is probably coin or sterling silver and it has hand engraved details.
That would make sense, the house is a parsonage for the oldest church in our county, the church dates to the 1830's but the current building was built in 1893. The parsonage house was built in the 20's