Overview
The 166th Ohio Infantry (One Hundred Days’ Service) was an infantry regiment organized in Ohio for Federal service during the American Civil War. Mustered at Camp Cleveland on May 13 and 15, 1864, the regiment served as part of the Union Army in the Eastern Theater. The unit was composed primarily of men from the Ohio National Guard, drawn from Huron, Holmes, Medina, and Wayne counties. The regiment was mustered in for a service term of 100 days.
The 166th Ohio Infantry was assigned to garrison and defensive duties in the defenses of Washington, D.C., and did not participate in major field engagements. Its service was notable for supporting the Union’s efforts to free veteran troops for active campaigning during the summer of 1864.
Organization & Service
The 166th Ohio Infantry (One Hundred Days’ Service) was organized at Camp Cleveland, Ohio, on May 13 and 15, 1864. The regiment was formed from the 63rd Regiment, Ohio National Guard (Huron County); the 59th Battalion (Holmes County); the 79th Battalion (Medina County); and one company from the 52nd Battalion (Wayne County). Upon completion of organization and muster, the regiment was ordered to Virginia.
Upon arrival, the 166th Ohio Infantry was assigned to duty in the defenses of Washington, D.C. The regiment was stationed at several forts south of the Potomac River, including Forts Richardson, Barnard, Reynolds, Ward, and Worth, with regimental headquarters at Fort Richardson. Its primary responsibilities included garrison duty, manning fortifications, and supporting the defense of the capital. The regiment remained in this capacity until the expiration of its 100-day term. The 166th Ohio Infantry returned to Ohio and was mustered out of service on September 9, 1864.
Research This Regiment Further
If you’d like to explore this unit’s history in more depth, regimental histories and Civil War reference works offer valuable detail.
Engagements & Campaigns
- Garrison duty at Forts Richardson, Barnard, Reynolds, Ward, and Worth, Defenses of Washington, D.C. (May–September 1864)
Casualties
Specific casualty figures for the 166th Ohio Infantry (One Hundred Days’ Service) are not detailed in primary sources. The regiment did not participate in major battles and primarily performed garrison duty. Available records do not indicate significant losses.
Field Officers & Commanders
- Colonel Harrison G. Blake
- Lieutenant Colonel Randolph Eastman
- Major Robert E. Leggett
Regimental Roster
The full roster of the 166th Ohio Infantry (One Hundred Days’ Service), including officers and enlisted men, is available for genealogical and historical research. The roster provides details on company assignments and service records.
To view the complete roster, visit the 166th Ohio Infantry (One Hundred Days’ Service) Roster page.
Sources & References
- Official Records of the Union and Confederate Armies, Series I, Vol. 37, Part II
- Ohio Roster Commission, Official Roster of the Soldiers of the State of Ohio in the War of the Rebellion, Vol. 6
- Dyer, Frederick H., A Compendium of the War of the Rebellion
- The Union Army, Vol. 2 (Federal Publishing Company, 1908)