Danielson is a borough in the town of Killingly in Windham County, Connecticut. The population was 4,265 at the 2000 census.
According to the United States Census Bureau, the borough has a total area of 1.2 square miles (3.2 km²), of which 1.1 square miles (2.8 km²) is land and 0.1 square miles (0.3 km²) (9.02%) is water.
As of the census of 2000, there were 4,265 people, 1,699 households, and 1,029 families residing in the borough. The population density was 3,860.7 people per square mile (1,497.0/km²). There were 1,859 housing units at an average density of 1,682.8/sq mi (652.5/km²). The racial makeup of the borough was 89.40% White, 2.63% African American, 0.61% Native American, 2.74% Asian, 1.83% from other races, and 2.79% from two or more races. Hispanic or Latino of any race were 5.09% of the population.