As of 2000, there were 349,445 housing units at an average density of 807 per square mile (312/km²). The racial makeup of the county was 71.35% White, 14.20% African American, 0.25% Native American, 4.48% Asian, 0.04% Pacific Islander, 6.63% from other races, and 3.05% from two or more races. Hispanic or Latino of any race were 15.61% of the population. 64.1% were Whites of non-Hispanic origin. 71.7% spoke English, 14.4% Spanish, 3.5% Italian, 1.1% Portuguese and 1.1% French as their first language.
By 2006 the population was 68.12% White, 13.91% African-Americans, 5.58% Asian, 0.16 Native American and 12.23% of other or mixed race. 18.54% of the population was Latino or Hispanic of any race.
There were 337,142 households out of which 34.00% had children under the age of 18 living with them, 53.90% were married couples living together, 12.20% had a female householder with no husband present, and 30.20% were non-families. 25.70% of all households were made up of individuals and 10.30% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.21.
In the county the population was spread out with 25.00% under the age of 18, 7.20% from 18 to 24, 30.40% from 25 to 44, 23.50% from 45 to 64, and 14.00% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 91.70 males. For every 100 females age 18 and over, there were 87.30 males.
According to 2006 HUD data, the median income for a household of one person in the county was $67,555 and the median income for a family of four was $96,500.
According to Census data, the per capita income for the county in 1999 was $36,726. The Bureau of Economic Analysis lists Westchester in 2004 with the per capita income of $58,952, the eighth highest in the country. The Census Bureau reports that 6.40% of families and 8.7% (2003) of the population were below the poverty line, including 26.53% of those under age 18 and 7.60% of those age 65 or over.
The largest census reviewed area in Westchester County is the City of Yonkers, New York's fourth-largest city, with a population of almost 200,000. The smallest is the community of Scotts Corners in the town of Pound Ridge with a population of 624.
Westchester County is served by Interstate 87 (the New York State Thruway), Interstate 95, Interstate 287 and Interstate 684. Parkways in the county include the Bronx River Parkway, the Cross County Parkway, the Hutchinson River Parkway, the Saw Mill River Parkway, the Sprain Brook Parkway and the Taconic State Parkway. The Tappan Zee Bridge connects Tarrytown to Rockland County across the Hudson River. The Bear Mountain Bridge crosses the Hudson from Cortlandt to Orange County. The combination of these numerous highways, proximity to New York City, and the county's large population all lead to substantial traffic enforcement and very busy local courts.
The development corridors in the county have defined sections and follow transportation corridors. The main north-south corridors are, from west to east, the U.S. Route 9/Albany Post Rd/Broadway Corridor along the Hudson River from Yonkers in the South to Peekskill/Cortlandt in the North. The Saw Mill River Parkway Corridor traverses the county in a north-eastern path, beginning in Yonkers, and terminating at I-684 in Bedford, mostly following the path of the Putnam Branch of the New York Central Railroad, which was abandoned in March 1970 (and which has largely been replaced by a paved path known as the South County and North County Trailways). The Sprain Brook Parkway traverses the county's midsection from a point in Yonkers where it breaks off from the Bronx River Parkway until Hawthorne about 15 miles (24 km) north where it merges with the Taconic State Parkway and continues until I-90 near Albany. The Hutchinson River Parkway lines the eastern county, from the Bronx (terminating at the Long Island crossing - the Whitestone Bridge) until the Connecticut state line in Greenwich, where it becomes the Merritt Parkway. I-684 begins at a junction with the Hutchinson River Parkway and I-287 in Harrison, and continues north into Putnam County (with a brief stretch in Greenwich, Connecticut) through Bedford and North Salem. The eastern most corridor is the I-95/New England Thruway which traverses the county on the Long Island Sound, from the Pelhams through the Town of Rye and into Connecticut. The East-West corridors are the Cross County Parkway, which traverses the southern county from Yonkers in the west through New Rochelle in the east, terminating at the Hutchinson River Parkway. The Cross Westchester Expressway/I-287 is the mid-county corridor spanning from the Tappan-Zee Bridge in Tarrytown to the west to I-95/New England Thruway in the east. The northern-most corridor is that approximating the US-202 route from Cortlandt, and the Bear Mountain Bridge, to Lewisboro and the Connecticut border. But unlike the more southerly corridors, US-202 is for the most part not a limited-access highway and has frequent traffic lights.
Robert Moses and others once proposed a bridge connecting Westchester with Nassau County, most likely using I-287 to do so. Public opposition was fierce, and the New York state government abandoned the plan.
Commuter train service in Westchester is provided by Metro-North Railroad (operated by the Metropolitan Transportation Authority). Metro-North operates three lines in the county; west to east, they are the Hudson, the Harlem and the New Haven lines, each of which stops in the Bronx between Westchester and Manhattan. Amtrak serves Croton-Harmon, New Rochelle and Yonkers. There are proposals for a cross-county rail line to connect all three lines and provide easier access to Stamford, Connecticut.
The MTA also operates a ferry service between Haverstraw in Rockland County and Ossining. New York Water Taxi operates a ferry from Yonkers to Battery Park City and the Financial District in Manhattan.
Bus service is provided by the Bee-Line Bus System (operated by the Westchester County Department of Transportation) both within Westchester and to Manhattan (BxM4C). The MTA Bus Company also runs the BxM3 to and from Getty Square in Yonkers to Midtown Manhattan.
Westchester County Airport is adjacent to White Plains.