Danielson is a borough in the town of Killingly in Windham County, Connecticut, United States. The population was 4,051 at the 2010 census.
Danielson was originally named "Danielsonville" for Gen. James Danielson, the builder of the first house in the settlement. It was renamed Danielson in 1895.
Danielson is the site of two historic districts listed on the National Register of Historic Places:
- Danielson Main Street Historic District is a 20-acre (81,000 m2) historic district along Main Street, from Water Street to Spring Street. Architectural styles in the district include Colonial Revival and Italianate, as well as others. The Danielson Main Street Historic District was added to the National Register of Historic Places on April 8, 1992.
- Broad Street – Davis Park Historic District: roughly along Broad Street, from Dorrance Street to Winter Street, to the north of Danielson Main Street Historic District. Architectural styles represented include Stick/Eastlake, Queen Anne, and Colonial Revival. It was added to the National Register of Historic Places in 1998.
It additionally is home to the Temple Beth Israel synagogue, which was added to the National Register of Historic Places in 2003. Danielson is also home to the CT State Police barracks "D".