Suffolk and Nassau 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 geographically make up the island's western end.
Suffolk County is the easternmost county in New York State and the New York Metropolitan Area.
As of the census of 2000, there were 1,419,369 people, 469,299 households, and 360,421 families residing in the county. The population density was 1,556 people per square mile (601/km²). There were 522,323 housing units at an average density of 573 per square mile (221/km²). The racial makeup of the county was 84.60% White (78.8% White Non-Hispanic), 6.94% African American, 0.27% Native American, 2.45% Asian, 0.03% Pacific Islander, 3.65% from other races, and 2.06% from two or more races. Hispanic or Latino of any race were 10.53% of the population. Some main European ancestries in Suffolk county as of 2000: 28.33% Italian, 22.02% Irish, 16.95% German and 5.98% English.
By 2006 the racial or ethnic makeup of the county was 83.6% White (75.4% White Non-Hispanic). African Americans were 7.4% of the population. Asians stood at 3.4% of the population. 5.4% were of other or mixed race. Latinos were 13.0% of the population.
There were 469,299 households out of which 37.00% had children under the age of 18 living with them, 62.00% were married couples living together, 10.80% had a female householder with no husband present, and 23.20% were non-families. 18.30% of all households were made up of individuals and 7.80% had someone living alone who was 65 years of age or older. The average household size was 2.96 and the average family size was 3.36.
In the county the population was spread out with 26.10% under the age of 18, 7.60% from 18 to 24, 31.20% from 25 to 44, 23.30% from 45 to 64, and 11.80% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 95.90 males. For every 100 females age 18 and over, there were 92.80 males.
The median income for a household in the county was $65,288, and the median income for a family was $72,112. Males had a median income of $50,046 versus $33,281 for females. The per capita income for the county was $26,577. About 3.90% of families and 6.00% of the population were below the poverty line, including 6.70% of those under age 18 and 6.30% of those age 65 or over.
Suffolk County ranks at number 23 on the list of the most populous counties in the United States.
Suffolk County has the highest number of Italian American residents of any county in the United States.