Paul J. Allen was born on November 10, 1826, in Bernardston, Massachusetts, to Jonathan Allen and Betsey Bascom. His father died around 1836. He eventually moved to New Haven, Connecticut, and by 1850, he was working as a blacksmith. He married Sarah R. Boyle in Bernardston on May 13, 1851, and they had at least three children: Elizabeth, born around 1854; Sarah, born around 1859; and Grace, born around 1861. Allen enlisted in the Union army on August 12, 1862, and mustered in as a private in Company E of the 15th Connecticut Infantry on August 25.
The regiment took part in the Battle of Fredericksburg and spent the remainder of the war stationed along the Virginia and North Carolina coasts. He was promoted to corporal on May 20, 1863, and then to sergeant on April 13, 1864. Confederate forces captured him near Kinston, North Carolina, on March 8, 1865, but he was paroled soon afterward. He mustered out on June 27, 1865. Allen returned to New Haven after the war and resumed his work as a blacksmith. They returned to Bernardston sometime in the 1860s, and by 1870, he owned $1,200 of real estate and $300 of personal property. He applied for a federal pension in August 1890 and eventually secured one. The 1900 census listed him as a “Capitalist.” He died of “cerebral apoplexy” in Bernardston on March 20, 1909.