I did a quick search on the NPS Soldiers and Sailors System. I got hits for 8 James Youngs. There were 8 others that you can discount (James A., James B., etc). There wasn't a James N. Young though.

The choices are the 2nd, 7th, 10th, 28th, 34th, 38th, 39th Iowa Infantry Regiments, or the 6th Iowa Cavalry. You can find the Soliders & Sailors System at http://www.itd.nps.gov/cwss/index.html. It'll give you some basic information about the regiment (usually from Dyer's) and the National Archives files so you can order the soldier's records.

Good luck.