On April 29, 1776 he was commissioned Captain of the 3rd Company, 2nd York County regiment of Massachusetts militia. He was also Captain in Col. John Frost's regiment appointed to command men raised to reinforce the Continental Army in the Revolutionary War from December 13, 1776 to March 13, 1777 at New York.
In December 1776, Captain William Holbrook's company of sixty men were enlisted and drafted for the town of Kittery. They marched from the town on or about December 13, 1776 through Portsmouth, N.H., Lynn and Cambridge, Mass. and Providence, R.I. to Fairfield, Conn. The regiment was at Danbury, Conn. on December 28th, in Brig. General Jonathan Warner's brigade; Major General Benjamin Lincoln's division. The regiment arrived at Peekskill, N.Y. on the Hudson River on January 6, 1777, where the brigade was in command of Brig. General Jotham Moulton.
On January 10th the regiment was ordered by General Lincoln to march to North Castle, where it was on the 14th: on that date was ordered to Tarrytown by General Moulton, where it was on the 15th; on the 17th the brigade marched to Williams, Colonel Frost's regiment, acting as front, rear and flank guards for the marching column; they had some fighting with the enemy near Knight's Bridge on the 18th to the 21st; on January 24th, the regiment was ordered to Mile Square by General Moulton, and on January 29th the regiment returned to Tarrytown and Dobb's Ferry. Major General Heath commanded the American army in this vicinity on January 31st.
February 8th the regiment was ordered to Peekskill and to take orders from General McDougall; they were there the 13th, and Captains Holbrook and Perkins' companies were sent to Fort Constitution. The regiment was at Peekskill on March 12th and the men were ordered to return all equipment to the Continental store. They marched for home, arriving at Kittery on March 23rd.
