Roger Averill was born in Salisbury, Connecticut. Some of his ancestors were among the earliest European settlers of Connecticut. His grandfathers, Samuel Averill and John Whittlesey, were natives of Washington, Connecticut. His parents, Nathaniel P. Averill and Mary Whittlesey, moved to Salisbury in 1805. He was one of seven children reared on a small farm, and his education was mainly of his own earning. He went to the common school and used a public library and prepared for college under the guidance of his brother Chester, who was a professor at Union College, and he graduated from that college with honour in 1832. He studied law and was admitted to the Bar in 1837. He opened his first practice in Salisbury, but attained a more successful practice after moving to Danbury in 1849.
He married Maria D. White, of Danbury, in October, 1844. Four of their children survived him and all of his sons also became lawyers.
Roger Averill fulfilled many functions in public service, such as member of the Connecticut General Assembly. In the spring of 1861, he was a prominent leader of the political party which opposed the election of Abraham Lincoln for President. However, the instance that he heard the news of the assault of Fort Sumter, he hastened to raise his flag and refuse any compromise or surrender. From then on, he devoted himself to the success of the Union army. He was elected Lieutenant Governor of Connecticut in the spring of 1862 and continued in that function throughout the war, during the last four of the eight years in which William A. Buckingham was Governor of the state, until 1866.
Averill's wife Maria died in February 1860. In September 1861, he married Mary A. Perry, of Southport, who survived him.
After the time as lieutenant governor, Averill was one of the organizers of the American Bar Association and was for many years acting chairman of the bar of his home county.
He died in Danbury, December 9, 1883, aged 74.
- Brief Descriptions of Connecticut State Agencies, Lieutenant Governor
- Memorials of Connecticut Judges and Attorneys, Obituary Notice of Roger Averill, As Printed in the Connecticut Reports
volume 50, pages 620-622