The Fifteenth Regiment of New Jersey Volunteers was one of five regiments of infantry furnished by the State under the call of the President of the United States for three hundred thousand men, issued July 1st, 1862. 

The New Jersey authorities took action without delay.   Governor Olden issued a proclamation July 8, 1862, in which he appealed to all citizens of the State, "that they see to it that New Jersey responds heartily and quickly to the call thus made upon it to to maintain the existence of the nation."   The number of regiments assignable to the State had not yet been made known, but to avoid delay, he called at once for four regiments of infantry - one from each of the four military divisions.  One of these military divisions comprised the counties of Warren, Sussex, Somerset, Morris, and Hunterdon.

...never was a regiment so quickly enlisted in the State.  Sussex County furnished three companies, Warren, Hunterdon, and Morris, each two; and Somerset one.

---- "The History Of The Fifteenth Regiment New Jersey Volunteers", Alanson A. Haines, 1883. 

New!!! The History Of The 15th NJVI was written by Haines, Captain James MacDonald (Company B), and Regimental Adjutant Halsey in 1883, and captures the war-time experiences of the 15th as they saw it happen. Reprints of the book are now available on-line at Amazon.Com. Click below to buy the book.