The 12th congressional district (together with the 11th district) was created starting with the
63rd United States Congress in 1913, based on redistricting following the
1910 United States census. In 1925,
Mary Teresa Norton was elected to the district and became the first female Democrat in the United States Congress. Historically, the 12th and its predecessors had been a swing district. However,
redistricting following the
2000 United States census gave the district a somewhat bluer hue than its predecessor. It absorbed most of Trenton, along with a number of other municipalities. Since then, the 12th has become a Democratic-leaning district, as measured by the Cook PVI. The redistricting made second-term Democrat
Rush D. Holt Jr. considerably more secure; he had narrowly defeated freshman Republican
Michael Pappas in 1998, and had only held on to his seat against
Dick Zimmer who represented the district from 1991 to 1997, by 651 votes in 2000. In 2002, despite an expensive challenge from former
New Jersey Secretary of State Buster Soaries, Holt was re-elected with 61% of the vote. The district became even more Democratic after redistricting following the 2010 census, as it lost its share of Republican-leaning
Hunterdon County and
Monmouth County, while being pushed further into strongly Democratic
Middlesex County and gaining the overwhelmingly Democratic
Union County town of
Plainfield, as well as the portion of Trenton that it had not absorbed in the previous redistricting. Holt retired in 2014 and was succeeded by State Assembly Majority Leader
Bonnie Watson Coleman, making her the first African-American woman elected to Congress from New Jersey. ==Counties and municipalities in the district==