In 1882, the Gilmores moved briefly to St. Louis, Missouri, and then to Chicago, Illinois, for his father's job with Carson Pirie Scott & Co. Gilmore attended school on Chicago's West Side, and played sandlot baseball.

[1] Gilmore worked as a messenger for Armour and Company after he graduated, earning $3 a week.

When the Spanish–American War began, he enlisted in the United States Army, and was deployed to Cuba in the 1st Infantry Regiment.

He developed a fever and lost 70 pounds (32 kg) in 46 days, and took 13 months to recover.

[6] By the end of the 1913 season, most Federal League teams were approaching bankruptcy.

[7] After the 1913 season, Gilmore convinced wealthy magnates to become team owners, including luring Charles Weeghman to take ownership of the Chicago franchise.

[10] During the Federal League's annual meeting after the 1914 season, Gilmore was re-elected president to a five year term.

[2] Gilmore enlisted in the Army in October 1918 and served with the Motor Transport Corps in World War I.