9th Massachusetts Infantry Regiment

9th Regiment Massachusetts Volunteer Infantry
Statue of Colonel Thomas Cass standing in the Boston Public Garden
Active	11 June 1861 – 21 June 1864
Country	United States of America
Allegiance	Union
Branch	United States Army
Type	Infantry
Size	1,650
Part of	In 1863: Sweitzer's Brigade, Barnes's Division, V Corps, Army of the Potomac
Motto(s)	"The Fighting Ninth"
Engagements	Siege of Yorktown Battle of Hanover Court House Battle of Mechanicsville Battle of Gaines's Mill Battle of Malvern Hill Second Battle of Bull Run Battle of Antietam Battle of Fredericksburg Mud March Battle of Chancellorsville Battle of Gettysburg Bristoe Campaign Battle of the Wilderness Battle of Spotsylvania Court House Battle of Cold Harbor
Commanders
Notable commanders	Col. Thomas Cass Col. Patrick Robert Guiney
Insignia
V Corps badge

The 9th Regiment Massachusetts Volunteer Infantry was a military unit from Boston, Massachusetts, USA, part of the Army of the Potomac during the American Civil War. It is also known as "The Fighting Ninth". It existed from 1861 to 1864 and participated in several key battles during the war. The unit is an Irish heritage unit, with many volunteers having been born in Ireland.