Upon graduation he was commissioned a brevet second lieutenant in Ordnance and his first assignment was at the Watervliet Arsenal in Troy, New York.

Following the bombardment of Fort Sumter, Sill resigned his teaching position and offered his services to the Governor of Ohio, who appointed him Assistant Adjutant General of the State in May 1861.

When the conference adjourned and the attendees began to disperse, Sill and Sheridan mistakenly put on each other's coats.

[2] Sill's body was found by Confederate troops, who buried it in a battlefield cemetery near the scene of his death.

Sill was later interred at Grandview Cemetery, Chillicothe, Ross County, Ohio.

"[4] In 1869, Sill's West Point classmate and division commander, General Philip H. Sheridan, officially established a military post in the Wichita Mountains of Oklahoma.