Allcock emigrated to the United States in 1845, settled in New York and opened a small drug store under the Astor House.

Allcock joined the New York State Militia, and was appointed Captain on 27 October 1856 with the Second Brigade, a post he held until the outbreak of the American Civil War.

[3] Allcock was engaged in the battles of the Wilderness, Spotsylvania, North Anna, Totopotomoy, Hanover Court House, Cold Harbor, Petersburg, first and second Deep Bottom, Weldon Railroad, and Ream's Station.

Allcock was wounded while in command of the Third Battalion at the First Battle of Ream's Station on 25 August 1864, for which he was appointed brevet colonel.

[5] Allcock returned to New York after the war and joined up with Benjamin Brandreth in the manufacturing and sale of popular patent medicines.