Pennington is a borough in Mercer County, New Jersey, United States. As of the 2010 United States Census, the borough's population was 2,585, reflecting a decline of 111 (-4.1%) from the 2,696 counted in the 2000 Census, which had in turn increased by 159 (+6.3%) from the 2,537 counted in the 1990 Census.
According to an 1883 history, "the first name of the village was Queenstown, which was given it in honor of Queen Anne. Later it was by some, in derision of its comparative insignificance, Pennytown, and as early as 1747 it began to be called Pennington." The name "Penington" was already known in the area, as Edward Penington (1667-1701), son of the British Quaker leader Isaac Penington, was appointed by his kinsman William Penn as Surveyor General of Pennsylvania. His father-in-law was a longtime leader, including as Governor, of the province of West Jersey, where Edward married. Henry Gannett attributes the borough's name to colonial governors from the Pennington family.
Pennington was established as a borough by an act of the New Jersey Legislature on January 31, 1890, from portions of Hopewell Township, based on the results of a referendum held on January 21, 1890. It is a dry borough, where alcohol cannot be sold.
According to the United States Census Bureau, the borough had a total area of 0.96 square miles (2.50 km2), including 0.96 square miles (2.49 km2) of land and <0.01 square miles (0.01 km2) of water (0.31%).
The borough is an independent municipality completely surrounded by Hopewell Township, making it part one of 21 pairs of "doughnut towns" in the state, where one municipality entirely surrounds another.
According to the Köppen climate classification system, Pennington, New Jersey has a hot-summer, wet all year, humid continental climate (Dfa). Dfa climates are characterized by at least one month having an average mean temperature ≤ 32.0 °F (≤ 0.0 °C), at least four months with an average mean temperature ≥ 50.0 °F (≥ 10.0 °C), at least one month with an average mean temperature ≥ 71.6 °F (≥ 22.0 °C), and no significant precipitation difference between seasons. During the summer months, episodes of extreme heat and humidity can occur with heat index values ≥ 100 °F (≥ 38 °C). On average, the wettest month of the year is July which corresponds with the annual peak in thunderstorm activity. During the winter months, episodes of extreme cold and wind can occur with wind chill values < 0 °F (< -18 °C).