Jacob Burnet McLean was born on August 10, 1841, in France to Nathaniel C. McLean and Caroline Thew. His father was a lawyer who owned $150,000 of real estate and $27,000 of personal property by 1860. He grew up and attended school in Cincinnati, Ohio, and his mother died sometime in the 1850s. He attended Harvard Law School in the 1860s. He travelled to Europe in 1869, and his passport application described him as 5 feet, 4 inches tall, with dark brown hair and hazel eyes.
He married Mary J. Hazlett on February 21, 1876, and they had at least seven children: Eloise, born around 1877; Hazelet, born around 1879; Mary, born around 1880; Rebecca, born around 1882; Frances, born around 1886; Jacob, born around 1891; and Nathaniel, born around 1894. They lived in Lake City, Minnesota, and McLean worked as a banker. By 1911, he was living in his son Hazelet’s household in Regina, Canada. He returned to Lake City in the 1910s, and he died there on May 31, 1926.