Killingly is located in the northeast of Connecticut in Windham County. The town was settled in 1700 and was incorporated 8 years later. Originally, the town was formed from mill villages on the banks of waterways, including the Five-Mile and the Quinebaug Rivers. Many of these villages still exist, and there are still two historical districts in their territory.
In the early 19th century, Killingly was the biggest producer of cotton goods in the state. In the early 20th century, the town became known worldwide for its curtain manufacturing industry.