McMillin married Marie Childress Brown, the daughter of Governor John C. Brown, in 1886.
 They had a son, John Brown McMillin (1887-1912) before she died the following year.
 In 1897, McMillin married Lucille Foster, a noted women's suffragist and president of the Tennessee Federation of Women's Clubs.
 She served as a civil service commissioner under President Franklin D. Roosevelt in the 1940s.
 She and McMillin had one daughter, Ellinor Foster McMillin Oliver (1898-1919).

McMillin's brother, Joseph, was a teacher at the Montvale Academy in Celina.
 One of his students was future Secretary of State Cordell Hull.
 Hull later recalled Benton McMillin as one of his political mentors.
McMillin married Marie Childress Brown, the daughter of Governor John C. Brown, in 1886.  They had a son, John Brown McMillin (1887-1912) before she died the following year.  In 1897, McMillin married Lucille Foster, a noted women's suffragist and president of the Tennessee Federation of Women's Clubs.  She served as a civil service commissioner under President Franklin D. Roosevelt in the 1940s.  She and McMillin had one daughter, Ellinor Foster McMillin Oliver (1898-1919).
McMillin's brother, Joseph, was a teacher at the Montvale Academy in Celina.  One of his students was future Secretary of State Cordell Hull.  Hull later recalled Benton McMillin as one of his political mentors.
Benton McMillin