Situated between the small cities of Norwalk and Stamford, the town is a bedroom community with relatively few office buildings. Most workers commute to the adjacent cities, and many also work in New York City. Two Metro North railroad stations — Noroton Heights and Darien — link the town to Grand Central Terminal and the rest of the New Haven Line. Although Darien has an increasingly vibrant downtown, residents often shop at the big-box stores and chain stores in neighboring Norwalk and Stamford. For recreation, the town includes four small parks, two beaches on Long Island Sound, four country clubs, a hunt club, and two yacht clubs.
With a median home price of approximately $1 million, Darien is one of the most expensive places to live in North America, and was rated one of the best places to live in America by CNN in 2005.
The public library in Darien, the Darien Library, has consistently ranked in the top ten of its category in the HAPLR (Hennen's American Public Library Ratings) Index of libraries.
As of the census of 2000, there were 19,607 people, 6,592 households, and 5,385 families residing in the town. The population density was 1,525.2 people per square mile (588.7/km²). There were 6,792 housing units at an average density of 203.9 persons/km² (528.3 persons/sq mi). The racial makeup of the town was 87.97% White, 0.45% African American, 0.04% Native American, 1.42% Asian, 0.03% Pacific Islander, 0.30% from other races, and 0.80% from two or more races. Hispanic or Latino of any race were 2.19% of the population.
There were 6,592 households out of which 46.4% had children under the age of 18 living with them, 74.5% were married couples living together, 5.6% had a woman whose husband did not live with her, and 18.3% were non-families. 15.6% of all households were made up of individuals and 8.3% had someone living alone who was 65 years of age or older. The average household size was 2.95 and the average family size was 3.31.
In the town the population was spread out with 32.5% under the age of 18, 3.0% from 18 to 24, 28.2% from 25 to 44, 24.0% from 45 to 64, and 12.4% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 96.2 males. For every 100 females age 18 and over, there were 89.7 males.
According to a 2007 estimate, the median income for a household in the town was $160,274, and the median income for a family was $195,905. As of the 2000 Census, males had a median income of $100,000 versus $59,313 for females. The per capita income for the town was $77,519. 2.0% of the population and 0.6% of families were below the poverty line. Out of the total people living in poverty, 1.6% are under the age of 18 and 2.6% are 65 or older.
The town is served by two train stations, the Noroton Heights and the other in downtown Darien. The Connecticut Turnpike runs through town, as does the Post Road, U.S. Route 1. Just to the north of town, the Merritt Parkway, Route 15 runs roughly parallel to the northern border between Darien and New Canaan. The Talmadge Hill railroad station is just north of the border as well. Along with the Post Road, major east-west thoroughfares in town are West Avenue and Middlesex Road. Major north-south roads are Hoyt Street, Hollow Tree Ridge Road, Nearwater Lane, Noroton Avenue, Middlesex Road, Mansfield Avenue and Brookside Road.
Interstate 95 has rest stops in Darien both for the southbound and northbound lanes. The state Department of Transportation has added "speed change" lanes between entrances and exits up to Exit 10 (and points westward). The phase of the highway widening from Exit 9 to Exit 10, at a cost of $7.5 million, is expected to be complete by October 2007, state Transportation officials said in August of that year. The state is in the process of planning more such lanes through the rest of the highway in town in a project expected to cost $24.5 million. About 150,000 vehicles pass Exit 12 each day, according to the state Department of Transportation. The state was considering closing the southbound entrance for Exit 12 in 2008 during work on the project.
Chapter 14 of English author Nigel Williams 1994 travelogue From Wimbledon to Waco tells of his difficulties in reaching Darien from Interstate 95.
In December 2007 a 15-month, $5.5 million project was completed to add fourth (or "operational") lanes in each direction between the entrances and exits at Exits 10 and 11 in Darien. An earlier project added a fourth lane on the southbound side from the entrance at Exit 10 to Exit 8. After that lane was added, a state Department of Transportation study concluded that accidents were down on that stretch of the highway by 20 percent, amounting to about 160 fewer accidents per year. Construction of operational lanes at exits 11, 12, and 13 was expected to begin in the late spring of 2008.