Josiah Dunlap was born around 1839 in Poland, Ohio, to Alexander and Eliza Dunlap. His father was a farmer who owned $4,000 of real estate and $1,500 of personal property by 1860. The family lived in Boardman, Ohio, until the 1850s, when they moved to Lackawannock, Pennsylvania. By 1860, he was working as a farm laborer.
He enlisted in the Union army in August 1862, and he mustered in as a private in Company H of the 134th Pennsylvania Infantry. He was wounded in the Battle of Antietam on September 17, 1862, and surgeons amputated his arm. He was discharged for disability on September 20, 1862.
He returned to Lackawannock after leaving the army, and he married a woman named Eliza around 1863. They had at least three children: Josiah, born around 1867; James, born around 1869; and Alexander, born around 1871. He worked as a coal driller, and by 1870, he owned $1,000 of real estate and $200 of personal property. He died of “enlargement [of the] liver and heart disease” in Lackawannock on August 2, 1907.