William Mercer, son of Samuel and Hannah (Culbert) Mercer, was born in 1811 in Donegal, Ireland and immigrated to the United States in 1819 with his parents. The Mercers first settled in Livingston County, New York and the elder, a farmer, purchased four hundred acres of land in Hillsdale County, Michigan in 1835. William remained with his father until 1843, when he purchased one hundred thirty acres of his father's estate. William Mercer became prominently identified with the public interests of his community, and in 1844 he was elected Associate Judge of the Circuit Court, and held the position for four years. In 1845 he married Sarah Gamble of Livingston, New York. In 1850 Mercer was elected county judge. He held that position until it was abolished by provisions of the state constitution. He also served the county as justice of the peace and other minor offices for many years. William and Sarah Mercer had six children: David G. (b. February 1846), Samuel A. (b. November 1847), Elizabeth (B. March 1849), William W. (b. March 1853), John G. (b. December 1854), and Sarah (b. December 1858). William Mercer died on February 9, 1901 in Somerset Township, Hillsdale County, Michigan.