The Dayville Historic District encompasses a collection of mid-19th century architecture in the Dayville village of Killingly, Connecticut. It is clustered around the junction of Main and Pleasant streets, extending along Main to High Street. The area flourished in the mid-19th century, as a consequence of the railroad being routed nearby, serving area textile mills. The district, residential except for a church, was added to the National Register of Historic Places in 1988.