|— Borough —|
|• Total||1.2 sq mi (3.2 km2)|
|• Land||1.1 sq mi (2.9 km2)|
|• Water||0.1 sq mi (0.3 km2)|
|Elevation||223 ft (68 m)|
|• Density||3,860.7/sq mi (1,490.6/km2)|
|Time zone||Eastern (EST) (UTC-5)|
|• Summer (DST)||EDT (UTC-4)|
|GNIS feature ID||0206590|
According to the United States Census Bureau, the borough has a total area of 1.2 square miles (3.1 km2), of which 1.1 square miles (2.8 km2) is land and 0.1 square miles (0.26 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.
The borough of Danielson and the town of Killingly are home to a small Laotian community. Both Danielson and Killingly are on the nation's list of top 50 cities with the highest percentage of citizens claiming Laotian ancestry.
There were 1,699 households out of which 33.3% had children under the age of 18 living with them, 37.1% were married couples living together, 17.2% had a female householder with no husband present, and 39.4% were non-families. 29.8% of all households were made up of individuals and 10.4% had someone living alone who was 65 years of age or older. The average household size was 2.45 and the average family size was 3.01.
In the borough the population was spread out with 27.2% under the age of 18, 10.8% from 18 to 24, 32.8% from 25 to 44, 18.6% from 45 to 64, and 10.6% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 95.2 males. For every 100 females age 18 and over, there were 90.0 males.
The median income for a household in the borough was $31,969, and the median income for a family was $40,990. Males had a median income of $31,315 versus $23,988 for females. The per capita income for the borough was $16,042. About 9.8% of families and 13.1% of the population were below the poverty line, including 11.8% of those under age 18 and 13.8% of those age 65 or over.
Historic districts 
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 Dorrane 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.
Media related to Danielson, Connecticut at Wikimedia Commons
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