Big Rock was a hamlet named for a massive boulder and located at the crossroads of present-day M-32 and Thornton Road. Seth Gillet became its first postmaster in 1882. By 1902, a general store owned by Briley Township pioneer William Remington housed the post office. At that time, Big Rock also had a church and school, a grange hall, a sawmill, and a blacksmith shop. The post office closed in 1920.