1st Regiment, New York Mounted Rifles (Sometimes designated 7th New York Cavalry.)

United States  U.S. Military   New York    New York Military   New York in the Civil War    1st Regiment, New York Mounted Rifles (Sometimes designated 7th New York Cavalry.)

Brief History
The New York State Military Museum website has a unit history project page for the 1st Infantry Regiment.

The Civil War in the East website gives a timeline for the involvement of 1st New York Infantry Regiment in the war.

1st Regiment, New York Mounted Rifles (Sometimes designated 7th New York Cavalry.) mustered in by companies. It mustered out 6th, 7th and 8th Companies July 10, 1865, 9th Company August 5, 1863.

Companies in this Regiment with the Counties of Origin
Men often enlisted in a company recruited in the counties where they lived though not always. After many battles, companies might be combined because so many men were killed or wounded. However if you are unsure which company your ancestor was in, try the company recruited in his county first.