b. June 21, 1811, in Otsego County, New York; d. March 27, 1887, in Springfield, Illinois. Samuel H. Treat studied law and was admitted to the bar in New York. In 1834, he moved to Illinois and settled in Springfield. Treat became one of the founding members of St. Paul’s Episcopal Church in 1835, and he married Ann Bennett at the church in 1837. Governor Thomas Carlin appointed Treat as judge of the Eighth Judicial Circuit in May 1839. When the Democratic majority of the Illinois General Assembly expanded the Illinois Supreme Court from four to nine members, they elected Treat as one of the new associate justices in February 1841. Each justice presided over county circuit courts in a specific region, and Treat was responsible for the Eighth Judicial Circuit in the east-central portion of the state. The new Illinois Constitution of 1848 reduced the size of the supreme court to three elected justices and relieved them of circuit court duty. David Davis replaced Treat on the circuit, but Treat retained his seat on the Illinois Supreme Court and became its chief justice. As judge of the circuit courts of the Eighth Judicial Circuit, Treat presided in at least nine hundred cases in which Lincoln was an attorney. During his tenure on the supreme court, Treat was a justice in 167 cases in which Lincoln was an attorney.

In March 1855, President Franklin Pierce appointed Treat to the position of judge of the newly created United States District Court for the Southern District of Illinois, a position he held for more than thirty years. As a federal judge, Treat presided over 139 cases in which Lincoln represented clients. Treat served continuously in the judiciary for forty-eight years.