You didn't say whether Matson was Mary's maiden name, or married name from first marriage. I found a Mary on the 1900 census Hill Co, TX living with her son James. If that is your Mary, this looks like the James from the census record. I'm posting this information so some of the others who have access to more sources than I do might be able to build on this. Or, disprove it.
TX Dth Idx thru 1976:
Name: James Vardeman Matson Death Date: 15 Jun 1931 Death Place: Waco, Mclennan, Texas Gender: Male Race: White Death Age: 72 years 4 months Estimated Birth Date: Birth Date: Feb 1859 Birthplace: Texas Marital Status: Married Spouse's Name: Father's Name: James Vardeman Matson Father's Birthplace: Mo. Mother's Name: Mary Lincecum Mother's Birthplace: Occupation: Banker Place of Residence: Hubbard, Texas Cemetery: Hubbard Cemetery Burial Place: Burial Date: 17 Jun 1931 Additional Relatives: X Film Number: 2135602 Digital Film Number: 4163597 Image Number: 1838 Reference Number: 29975 Collection: Texas Deaths, 1890-1976
Using maiden name of the above Mary I found one more:
Name: S. M. Lewis Death Date: 14 Dec 1924 Death Place: Hubbard, Hill, Texas Gender: Female Race: w Death Age: Estimated Birth Date: Birth Date: 27 Feb 1855 Birthplace: Texas Marital Status: Widowed Spouse's Name: Father's Name: J.V. Matson Father's Birthplace: Missouri Mother's Name: Mary Lincecum Mother's Birthplace: Mississippi Occupation: Housewife Place of Residence: Cemetery: Burial Place: Hubbard Burial Date: 15 Dec 1924 Additional Relatives: Film Number: 2113743 Digital Film Number: 4165528 Image Number: 808 Reference Number: 39289 Collection: Texas Deaths, 1890-1976
I'm guessing the above is the Sallie in the family below.
1860 census Washington Co, TX:
Matson, James, 39, b MO " Mary, 34, bMS " Mary, 9, b TX " Sallie, 7, b TX " Richard, 4, b TX " James, 2, b TX
Maybe someone can track down descendants of the above. You never know who the family may have heard the old stories and know something about J.H. Horn????
Aha, go to -- http://www.findagrave.com/http://www.findagrave.com/ -- Do a cemetery search for Fairview Cemetery in Hill Co, TX. Enter last name of Matson and you'll find members of the family buried there. I didn't look at all the entries, but someone knows something about the family because they have the maiden name for Mary, and more. You might try contacting the people who have entered the additional information.