Sidney Edgerton was born at Cazenovia, New York, on August 17, 1818. He moved to Ohio in 1849 and studied law in Akron, Tallmadge, and Cincinnati. An active politician during the 1850s, he was one of the members of the convention which formed the Republican Party in 1856 and was elected to Congress in 1858 and 1860.

In 1863, he received the appointment as chief justice of the newly formed territory of Idaho which then included Montana. He left Akron, Ohio, on June 1, 1863, accompanied by his wife Mary and their children, his nephew, Wilbur F. Sanders, and several others. They traveled the Missouri River by steamboat to Omaha, where they joined a party going to Lewiston, Idaho. The group traveled by ox wagon via the Platte River, Fort Laramie, South Pass, and Red Rock into Bannack where they were forced to stop on September 17, 1863, because of the onset of winter weather. Sidney Edgerton returned to Washington in the fall of 1863, carrying gold in the lining of his coat to display to congressmen, and succeeded in getting a bill passed creating the territory of Montana and defining its present boundaries. On the return trip, he learned of his appointment by Lincoln as the first governor of Montana Territory. He held that position until July 1865, when he took his family back to Ohio. He died in Akron, Ohio, July 19, 1900, at the age of 82.

The members of Edgerton's family and wagon-train party were also to become prominent in Montana. Wilbur F. Sanders became a famous vigilante and politician and was Montana's first U.S. Senator. Martha Edgerton Rolfe Plassmann, the oldest daughter, became a writer of early Montana history, and Lucia Darling, a niece, has often been credited with having been Montana's first school teacher.