The following is taken from New York in the War of the Rebellion, 3rd ed. Frederick Phisterer. Albany: J. B. Lyon Company, 1912.

This regiment, Col. William A. Jackson, was accepted by the State and received its numerical designation May 13, 1861; was organized at Albany, and there mustered in the service of the United States for two years May 17, 1861. May 11, 1863, the three years' men of the regiment were transferred to the 121st N. Y. Volunteers.
The companies were recruited principally: A and E at Schenectady; B, F, H and I at Albany and immediate vicinity; C at Fishkill; D— The regiment left the State June 19, 1861; served at Washington, D. C., from June 21, 1861; in 2d Brigade, 5th Division, Army of Northeastern Virginia, from July 13, 1861; in Franklin's Brigade, Division of Potomac, from August 4, 1861; in Newton's Brigade, Franklin's Division, Army of the Potomac, from October 15, 1861; in 3d Brigade, 1st Division, 1st Corps, Army of the Potomac, from March 13, 1862; in the 3d Brigade, 1st Division, 6th Corps, Army of the Potomac, from May, 1862, and, commanded by Col. George R. Myers, was honorably discharged and mustered out at Albany May 28, 1863.
During its service the regiment lost by death, killed in action, 3 officers, 28 enlisted men; of wounds received in action, 1 officer, 7 enlisted men; of disease and other causes, 1 officer, 35 enlisted men; total, 5 officers, 70 enlisted men; aggregate, 75; of whom 3 enlisted men died in the hands of the enemy.

The following is taken from The Union army: a history of military affairs in the loyal states, 1861-65 -- records of the regiments in the Union army -- cyclopedia of battles -- memoirs of commanders and soldiers. Madison, WI: Federal Pub. Co., 1908. volume II.

Eighteenth Infantry.—Cols., William A. Jackson, William H. Young, George R. Myers; Lieut.-Cols., William .H. Young, George R. Myers, John C. Maginnis; Majs., George R. Myers, John C. Maginnis, William S. Gridley. The 18th, the "New York State Rifles," was composed of two companies from Schenectady, four from Albany, one from Dutchess county, one from Orange county.v one from Ontario county and one from St. Lawrence county. It was mustered into the U. S. service at Albany, May 17, 1861, for a period of two years, and left the state for Washington on June 18, after a month in camp near Albany. Camp on Meridian hill was occupied until July 12, when the regiment was ordered to Alexandria and became a part of the 2nd brigade, 5th division, Army of Northeastern Virginia. It advanced with the army to Manassas, encountered the enemy on the Braddock road, at Fairfax Station and Blackburn's ford, and participated in the Bull Run battle as support for artillery. It was then withdrawn to Alexandria; on Aug. 4, was assigned to Franklin's brigade, later commanded by Gen. Newton; and then went into camp near Fairfax seminary, where the construction of Fort Ward occupied the troops. On March 10, 1862, the regiment was ordered to Fairfax Court House, but immediately returned to camp, and in April, with the 3d brigade, 1st division, 6th corps, Army of the Potomac, moved to Bristoe Station. Again the regiment was ordered to return to camp and it finally reached Yorktown at the time of its evacuation by the Confederate forces. It was active at West Point and in the Seven Days' battles, its loss being heaviest in the battle of Games' mill. It was then stationed at Harrison's landing until Aug. 15, when it was ordered to Newport News and on the 24th reached Alexandria. It was engaged at Crampton's gap, Antietam and Fredericksburg, after which it went into camp near Falmouth, until called upon to participate in the "Mud March" and in the Chancellorsville campaign. At Marye's heights and Salem Church the 18th was closely engaged and lost heavily. This was the last battle of the regiment, which was soon after ordered home and was mustered out at Albany, May 28, 1863, the three years men being assigned to the 121st N. Y. The death loss during service was 39 from wounds and 36 from other causes.