Mary Clap Blake was born in Boston, Massachusetts, in January 1831, the daughter of James Blake and Polly Clap. She had two brothers, James Barnard Blake (1827-1870) and Gorham Blake (1829-1897). In 1859, Mary married Edward James Young (b. 1829), who graduated from Harvard College in 1848, attended Harvard Divinity School from 1850 to 1852, and studied at the German Universities of Göttingen and Halle between 1852 and 1856. After returning to the United States, Young preached at Channing Church in Newton, Massachusetts, a position he held until 1869, when he became a professor of Hebrew and Biblical literature at Harvard. In 1880, they moved to Waltham, Massachusetts, where Edward was pastor of the First Parish Church. Mary and Edward had at least four children: Edward B., Edith, Herbert, and Charles. Mary Blake Young died on October 21, 1901, and Edward James Young died in 1906.
Gorham Blake, Mary's brother, was born on May 26, 1829, and became a superintendent of iron mines in Vermont in 1851. The following year, he moved to California. He continued to work in the mining industry until 1855, when he opened an assaying business with John Agrell in Sacramento; the company became Blake & Co. later that year. In the late 1860s, Blake lived in Georgia, where he had mining interests. He earned a medical degree around 1877 and married Mary A. Gordon in Fulton, Georgia, on May 9, 1885, though they later moved to California. Gorham Blake died in Oakland, California, California, on December 17, 1897.