I am looking for information on both John and Mary. I think that John was born about 1810 and Mary was born about 1809 in what is believed to be Mercer Maine. Her parents may be Joseph and Martha Kimball Williamson. She had siblings, Joseph, Jr., Love, William K., and Abigail. On Jan. 17, 1832 a Mary Williamson married a John Brown in Industry, Me. (I have no proof that this is my Mary, but the location and time frame are right). In the 1880 census Mary Brown is listed in the home of her brother Joseph, Jr. I don’t know if her husband died or if, perhaps, they divorced or if Mary was just visiting. I have no death date for Mary.
Possible Mary Brown burial based on data from family trees on ancestry, I believe this may be your Mary. There are also a Joseph and Martha Williamson memorials here. However I didn't see a John Brown buried here that would fit the time frame. (New Sharon Me. is just a few miles from Mercer Me.)