Sullivan County Courthouse is located at 414 Broadway, Monticello NY 12701; phone: 794‑4066.
In the year 1803 the town of Thompson was incorporated, and was so named after Judge William A. Thompson. In 1802 Judge Thompson was appointed by Governor George Clinton one of the judges of the common pleas of Ulster County, and in the following year he was the first judge of that county. When Sullivan county was erected he was its chief magistrate, and remained so until 1823, when he became ineligible by reason of his age, and was succeeded by Livingston Billings. Judge Thompson, a native of the state of Connecticut, was the son of William A. Thompson, who was among the first settlers in this territory. The son became one of the distinguished men of that part of the state, and, after the termination of his official career as chief magistrate of the county, he achieved fame for his scientific and philosophical researches. He died in December, 1847.
In 1804, John P. Jones and his brother, Samuel Jones, made a clearing and erected a saw mill in the woods west of the center of the town of Thompsonville, which Judge Thompson had founded and named. They planned a village there and named it Monticello, and from this small beginning in time developed the present county seat of Sullivan.
Gradually the village of Monticello increased in population and importance, and it was not many years before it became essentially the center of the county activity. Soon after the act to organize the county became a law, several new buildings were erected in Monticello, among them a tavern which provided for a court room on its second floor. This tavern was owned by Curtis Lindley, and there the county courts were held and sometimes the circuit courts. Before 1809 a triangular contest began between Liberty, Thompsonville and Monticello in regard to securing the county buildings. The site of the court house and jail was left to be determined by commissioners appointed by the governor, William Ross and Joseph Morrell, of Orange County, and Abraham H. Schenck, of Dutchess, and this commission decided in favor of Monticello. In 1810 a commission was appointed to raise money for building the court house and jail and superintend the erection of the buildings, but there was so much opposition to the measure that it was not until January, 1814, nearly five years after the erection of the county, that the small wooden building erected for the purpose was completed.