Mattie married Walter B. Reed on July 17, 1897 in Fairmont, Minnesota at the Fairmont Congregational Church where the Rev. Dickenson performed the ceremony. The following day, a wedding dinner was hosted at the home of Mattie's sister, Winnefred (Mrs. Steven Barnett). A few months later, the newlyweds started housekeeping in the home of a bachelor farmer, Jim Thompson. In 1900, Mattie's in-law's retired from their farm in Emmett County, Iowa, so she and Walter took over the farm for the next four years. They then moved to the Gillmore farm, just south of the Minnesota state line and lived there for the next ten years. Mattie and Walter next purchased the Anderson farm, which was southwest of Ceylon, Minnesota and near the Champine homestead, and lived there until 1920. The Reed children attended school in District #17, generally known as the Foell School. In 1920, the family moved to a larger farming operation and a warmer climate, having purchased a fruit and stock ranch just south of Parker in Linn County, Kansas. Although Mattie loved the warmer weather in Kansas, the ranch did not turn out to be very profitable, so they returned to Iowa.

Mattie's granddaughter, Ione Early, remembers Mattie as being "the best cook this side of heaven". In order to help with financial struggles during the Great Depression, Mattie opened a little restaurant in Mankato, Minnesota. Ione would take the train, from her home in Kansas City, to Mason City, Iowa where Mattie and Walter would meet her and then take her back to their home in Minnesota for the summer. They did this every summer for 5 or 6 years. Ione recalls playing the board game, Sorry, with Mattie and described her grandma and grandpa Reed as "wonderful grandparents, very warm, loving, hospitable people."
Mattie and Walter had been married for 55 years at the time of Mattie's death.

Mayflower Passenger Ancestor Line:
DEGORY PRIEST (1579 - 1621), Mayflower passenger, 8th great-grandfather
Mary Priest (1613 - 1689), Daughter of Degory Priest
John Pratt (1631 - 1698), Son of Mary Priest
Delivered Pratt (1664 - 1726), Daughter of John Pratt
Ruemourn Townsend (1698 - 1741), Son of Delivered Pratt
Sarah Townsend (1736 - 1808), Daughter of Ruemourn Townsend
John Alexander Hewlett (1775 - 1812), Son of Sarah Townsend
Samuel Hewlett (1775 - 1811), Son of John Alexander Hewlett
Hannah Hulett (Hewlit) (1802 - 1880), Daughter of Samuel Hewlett
Charles Samuel Champine (1832 - 1919), Son of Hannah Hulett (Hewlit)
Mattie Champine (1877 - 1953), Daughter of Charles Samuel Champine