The region in which Summit is located was purchased from Native Americans on October 28, 1664. Summit's earliest European settlers came to the area around the year 1710.

The original name of Summit was "Turkey Hill" to distinguish it from the area then known as "Turkey" (New Providence's original name until 1759) where turkeys were known to run wild. During the American Revolutionary War period, Summit was known as "Beacon Hill", because bonfire beacons were lit on an eastern ridge in Summit to warn the New Jersey militiamen of approaching British troops.

Summit was called the "Heights over Springfield" during the late 18th Century and most of the 19th Century, and was considered a part of New Providence.

As of the censusGR2 of 2000, there were 21,131 people, 7,897 households, and 5,606 families residing in the city. The population density was 1,348.5/km² (3,490.7/mi²). There were 8,146 housing units at an average density of 519.9/km² (1,345.7/mi²). The racial makeup of the city was 87.77% White, 4.33% African American, 0.09% Native American, 4.45% Asian, 0.01% Pacific Islander, 1.70% from other races, and 1.65% from two or more races. Hispanic or Latino of any race were 10.17% of the population.

In the city the population was spread out with 27.0% under the age of 18, 4.4% from 18 to 24, 33.0% from 25 to 44, 22.5% from 45 to 64, and 13.1% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 93.8 males. For every 100 females age 18 and over, there were 89.1 males.

The median income for a household in the city was $92,964, and the median income for a family was $117,053. Males had a median income of $85,625 versus $46,811 for females. The per capita income for the city was $62,598. About 2.5% of families and 4.2% of the population were below the poverty line, including 4.1% of those under age 18 and 4.3% of those age 65 or over.