Isaac Peckham Christiancy (March 12, 1812 – September 8, 1890) was chief justice of the Michigan State Supreme Court and U.S. Senator from the state of Michigan. Christiancy was born near Johnstown, New York in what is now Bleecker, New York to parents of humble means. His grandfather, Isaac Peckham, was one of the first pioneers in Caroga, New York, settling in the area as early as 1783. Christiancy attended the common schools and the Johnstown and Ovid Academies. After his father died when he was 13, he also had to support his family. He taught school and studied law. In 1836, Christiancy was admitted to the bar after moving to Monroe, Michigan, where he obtained a clerkship in a Federal land office. He married Elizabeth E. McClosky on November 16, 1839.