The 1st Regiment Massachusetts Volunteer Infantry was an infantry regiment in the Union Army during the American Civil War. Organized at "Camp Ellsworth" in Cambridge, Massachusetts, the regiment was made up partly of companies that had belonged to the First Regiment Massachusetts Volunteer Militia, a peactime unit of state militia. The companies were mostly from Boston but also Roxbury and Brookline. The First Massachusetts was the first of the Massachusetts regiments recruited for a term of three-years.