Nassau and Suffolk counties together are generally referred to as "Long Island" by area residents — as distinct from the New York City boroughs of Queens (Queens County) and Brooklyn (Kings County), which physically make up the island's westernmost end.
In 2005, Forbes magazine named Nassau County, along with Suffolk County, New York, as the safest region in the United States, with the lowest crime rate.
As of 2008, Nassau County is the second richest county per capita in the State of New York and the 10th richest in the nation, with a median household income of $85,994.
As of the census of 2000, there were 1,334,544 people, 447,387 households, and 347,172 families residing in the county. The population density was 4,655 people per square mile (1,797/km²). There were 458,151 housing units at an average density of 1,598 per square mile (617/km²). The racial makeup of the county was 79.30% White (73.95% White Non-Hispanic), 10.01% African American, 0.16% Native American, 4.73% Asian, 0.03% Pacific Islander, 3.57% from other races, and 2.12% from two or more races. Hispanic or Latino of any race were 10.09% of the population.
By 2006 the racial or ethnic makeup of the county was 74.3% White (69.1% White Non-Hispanic). African Americans were 11.3% of the population. 7.8% other or mixed race. Asians were up to 6.9% of the population. The Latino population had grown slightly faster than the African-American population and now was 12.1% of the population.
Italian Americans make up a large portion of Nassau, and there are numerous Italian communities throughout the county. The large Sikh population in Nassau County has built numerous Sikh Gurdwaras or temples; the two main ones are in Plainview and Glen Cove. The top 5 ancestories are 23% Italian, 14% Irish, 7% German, 5% American and 4% Polish. According to the Census Bureau, the population of the county has slightly decreased to 1,333,137 people in 2005, although it had increased to 1,339,641 in 2004.
There were 447,387 households, out of which 35.30% had children under the age of 18 living with them, 63.10% were married couples living together, 10.90% had a female householder with no husband present, and 22.40% were non-families. 18.80% of all households were made up of individuals and 9.40% had someone living alone who was 65 years of age or older. The average household size was 2.93 and the average family size was 3.34.
In the county the population was spread out with 24.70% under the age of 18, 7.30% from 18 to 24, 28.90% from 25 to 44, 24.00% from 45 to 64, and 15.00% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 92.80 males. For every 100 females age 18 and over, there were 89.00 males.
The median income for a household in the county was $72,030, and the median income for a family was $81,246 (these figures had risen to $87,658 and $101,661 respectively as of a 2007 estimate). Males had a median income of $52,340 versus $37,446 for females. The per capita income for the county was $32,151. About 3.50% of families and 5.20% of the population were below the poverty line, including 5.80% of those under age 18 and 5.60% of those age 65 or over.