Compounding the 12th Volunteers/12th Militia confusion is the fact that Butterfield at one point commanded the brigade in which the 12th New York Volunteers served.

The regiment was attached to Richardson's Brigade, Tyler's Division, McDowell's Army of Northeast Virginia, June to August 1861.

Butterfield's 3rd Brigade, Porter's 1st Division, III Corps, Army of the Potomac, to May 1862.

Men who had enlisted for three years' service were consolidated into two companies and served duty as Provost Guard for Headquarters of V Corps under the command of Captain Henry W. Ryder.

By the end of the first full year of hard campaigning, the regimented returned 720 Model 1842 smoothbore percussion muskets to the Adjutant General.