Lemuel Hallman Mattern was born on September 27, 1841, in Pennsylvania to Andrew and Sophia Mattern. His father was a waggoner who owned $700 of real estate in 1850. He grew up and attended school in West, Pennsylvania. He married Sarah Martin in the 1860s, and they had at least three children: Carrie, born around 1870; Lilly, born around 1873; and William, born around 1879.
They lived in Huston, Pennsylvania, and Mattern worked as a dry goods merchant. By 1870, he owned $5,000 of real estate and $1,400 of personal property. They moved to North Woodbury, Pennsylvania, in the 1870s. His wife died in the early 1880s, and he married a woman named Addie around 1883. Their daughter Louise was born around 1886. They moved to Indiana in the 1880s. By 1910, they were living in Whiting, Indiana, and Mattern owned a drug store. He died there of pneumonia on November 3, 1920.