Throughout most of the 17th century the chief inhabitants of the Killingly area were Native Americans. A fort had been constructed on a low hill in the Danielson area about 30 or 40 rods southeast of the “great falls” of the Quinebaug River. Native American tribes (including Nipmucks, Pequots, Mohegans and Narragansetts) considered these falls an important fishing place, calling the area “Acquiunk.”

The earliest settler within the Danielson area evidently was James Danielson. In 1707, he purchased the triangle of land between the Quinebaug and Five Mile Rivers (Assawaga), about 2000 acres, from Major James Fitch for 170 pounds. By 1770, William Danielson, later a Colonel in the Militia, had established an iron works on the Five Mile River in present-day Danielson. Boaz Sterns first settled the north end of modern day Main Street in the 1720s; other early family names of settlers in the area include Spaulding and Hutchins.

In the late 1700s, William Cundall established one of the earliest woolen works in Connecticut. By the 1830s there were many textile mills located along the Quinebaug and Five Mile Rivers. Killingly was considered the greatest cotton-manufacturing town in Connecticut in 1836. The firm of Powdrell & Alexander, operating six curtain factories in the town from the 1920s led the town to become known as “Curtaintown USA.”

During the 1800s Franklin Street was a main stagecoach road between Providence and Hartford and Broad Street / Green Hollow Road was the stage road from Norwich to Worcester.

The region around the Westfield meetinghouse developed into a thriving village. Following the opening of the Norwich & Worcester Railroad in 1840, population quickly shifted in the town to the area nearer the railroad. As prosperity returned to the town after the Civil War, the Borough undertook major construction projects. The first public high school (the old grammar school) on School Street was built along with the Music Hall (present Town Hall). Many large business blocks were completed. Gas and electric lighting and telephone service were provided along with a community water system.

The Borough of Danielsonville, formed in May 1854, also included a portion of East Brooklyn. This changed in May 1895, when the name of the Borough was shortened to Danielson and the western boundary was set at the Quinebaug River.

A new high school on Broad Street, dedicated in 1908 became so overcrowded that by 1965 a new facility on Westfield Avenue was opened. The old building became the Killingly Junior High School and is now utilized as the Killingly Community Center. A modern elementary school (Killingly Memorial) that consolidated some of the outlying one-room schools was dedicated in 1953. St. James Church also built a new parochial school to alleviate crowding.

In October 1963, the Borough of Danielson began operating under a new charter with a president and Borough Council.

Business blocks in the Borough continue to undergo façade improvements. What once was the principal hotel in Danielson, on Main Street since 1856, has undergone a complete renovation and emerged as the new Main Street Exchange. The latest large building project was the construction of the imposing State of Connecticut Superior Court House built where the first public high/grammar school once was just one block off Main Street on School Street.

Main Street businesses have pride in their shops and have organized to promote them. The central business district has been designated as a National Historic District.

Another source of pride in the town is the list of prominent natives who list Killingly as their birthplace. Dr. Sidney P. Marland, Jr. served his country as Commissioner of Education from 1970 to 1972. From 1972 to 1973 he was the nation’s first statutory Assistant Secretary of Education in the Department of Health, Education, and Welfare (a new post created by the Education Amendment of 1972.) Charles Lewis Tiffany, founder of Tiffany’s in New York, was born in Killingly. The first American woman to be issued a patent on May 5, 1809 for her invention of a “new and useful improvement in weaving straw with silk or thread.,” Mary Dixon Kies, was born in South Killingly.