On February 27, 1866, Sidway married Charlotte Spaulding (1843–1934), the only daughter of U.S. Representative Elbridge G. Spaulding (1809–1897).
Together they had five children:
Harold Spaulding Sidway (1868–), who married Mary Chase
Frank St. John Sidway (1869–1938), who married Amelia Minirva (Roberts) Sidway (1881–1972)
Edith Sidway (1872–1958), who married William Allen Gardner (1869–1941)
Clarence Spaulding Sidway (1877–1953), who married Genevieve Clark (Hingston) Sidway (1880–1939)
Ralph Huntington Sidway (1884–1936), who married Stephana Ostrom (Barnum) Sidway (1882–1962)
Sidway was a life member of the Buffalo Library, member of the Buffalo Historical Society, and former treasurer and a member of the Buffalo General Hospital Board.
He was also a trustee of the Forest Lawn Cemetery.
 Sidway had a keen interest in athletics and outdoor sports.
He was a member of the old Forester Gun Club and was a member of one of the first four oared rowing crews organized in Buffalo.
Sidway was president of the Archery Club of Buffalo, the Toxophilites, and was one of the organizers of the Niagara Base Ball Club, one of the first amateur base-ball clubs organized.
He was a member, and one time president, of the Buffalo Club and the Country Club of Buffalo.
In addition, he was president of the Falconwood Club for many years, which was founded by Lewis F. Allen in 1858.
Franklin and Charlotte enjoyed traveling, sailing on the St. Louis in 1899 between Southampton, England and New York City, and spending time at the Government House in 1895 in the Bahamas.

Franklin Sidway died March 7, 1920 was interred at Forest Lawn Cemetery, Buffalo.
On February 27, 1866, Sidway married Charlotte Spaulding (1843–1934), the only daughter of U.S. Representative Elbridge G. Spaulding (1809–1897). Together they had five children:
Harold Spaulding Sidway (1868–), who married Mary Chase
Frank St. John Sidway (1869–1938), who married Amelia Minirva (Roberts) Sidway (1881–1972)
Edith Sidway (1872–1958), who married William Allen Gardner (1869–1941)
Clarence Spaulding Sidway (1877–1953), who married Genevieve Clark (Hingston) Sidway (1880–1939)
Ralph Huntington Sidway (1884–1936), who married Stephana Ostrom (Barnum) Sidway (1882–1962)
Sidway was a life member of the Buffalo Library, member of the Buffalo Historical Society, and former treasurer and a member of the Buffalo General Hospital Board. He was also a trustee of the Forest Lawn Cemetery.  Sidway had a keen interest in athletics and outdoor sports. He was a member of the old Forester Gun Club and was a member of one of the first four oared rowing crews organized in Buffalo. Sidway was president of the Archery Club of Buffalo, the Toxophilites, and was one of the organizers of the Niagara Base Ball Club, one of the first amateur base-ball clubs organized. He was a member, and one time president, of the Buffalo Club and the Country Club of Buffalo. In addition, he was president of the Falconwood Club for many years, which was founded by Lewis F. Allen in 1858. Franklin and Charlotte enjoyed traveling, sailing on the St. Louis in 1899 between Southampton, England and New York City, and spending time at the Government House in 1895 in the Bahamas.
Franklin Sidway died March 7, 1920 was interred at Forest Lawn Cemetery, Buffalo.
Franklin Sidway