A special election was held in Connecticut's at-large district in 1817 to fill two vacancies in the 15th Congress, both of which had occurred before the start of that Congress. The vacancies were left by the death of Sylvanus Backus (F) on February 15, 1817 and by Charles Dennison (F).
Election results
As there were two vacancies in an at-large district, the top two candidates were elected to represent Connecticut
Huntington and Terry took their seats with the rest of the 15th Congress.
References
Connecticut's at-large congressional district special election, 1817 Wikipedia(Text) CC BY-SA