| Unit Name: | 3rd Connecticut Infantry Regiment |
| Dates: | May 14, 1861, to August 12, 1861 |
| Country: | United States |
| Allegiance: | Union |
| Branch: | Infantry |
| Battles: | First Battle of Bull Run |
The 3rd Connecticut Infantry Regiment was an infantry regiment that served in the Union Army during the American Civil War.
The 3rd Connecticut Infantry Regiment was organized at New Haven, Connecticut and mustered in for three-months service on May 14, 1861, under the command of Colonel John L. Chatfield.
The regiment was attached to Mansfield's command, Department of Washington, to June 1861. Key's 1st Brigade, Tyler's 1st Division, McDowell's Army of Northeastern Virginia to August 1861.
The 3rd Connecticut Infantry mustered out of service on August 12, 1861.
Left Connecticut for Washington, D.C., May 19. Duty at Camp Corcoran, defenses of Washington, D.C., until June 1, 1861. Advanced to Vienna and Falls Church, Va., June 1–3, and picket duty there until July 16. Advanced to Manassas, Va., July 16–21. Occupation of Fairfax Court House July 17. Battle of Bull Run, Va., July 21.