I do have a Mattie Mills listed. She was the oldest daughter of John Mills-son of Willis Mills. She is 2yrs in the 1880 census. She married a Hardcastle-had 2 children Alma & John. The 1920 Census for Coleman Co. TX shows Alma Hardcastle-12 & John Hardcastle-9 living with their grandparents-John & Josephine Mills. Not sure if Mattie was living at that time. Hope this helps.