[21] Sussex was incorporated as a borough by an act of the New Jersey Legislature on October 14, 1891, as Deckertown, from portions of Wantage Township.

[24][25] A joint commission of residents of both Sussex and Wantage had recommended that the two communities should be consolidated to form what would be called the Township of Sussex-Wantage, which would operate within the Faulkner Act under the council-manager form of government, with a mayor and a six-member township council, and that voters in both municipalities should approve a referendum to be held on November 3, 2009.

The committee noted that the two municipalities share common issues, schools, library and community services and that the artificial nature of the octagonal Sussex border often made it hard to distinguish between the two.

[31] The borough is in the watershed of the Wallkill River (which flows north, and empties into the Rondout Creek, which flows into the Hudson River near Kingston, New York) and its tributary Glen Brook, which near Sussex forms a small body of water called Clove Lake, part of which is within the borough.

Due to its inland location and elevation, Sussex has a climate much cooler than most of the state, classified as humid continental (Köppen Dfa, closely bordering on Dfb), with cold, moderately snowy winters, and very warm, humid summers.

[42] As of the 2000 United States census[16] there were 2,145 people, 903 households, and 512 families residing in the borough.

[7] The borough form of government used by Sussex is a "weak mayor / strong council" government in which council members act as the legislative body with the mayor presiding at meetings and voting only in the event of a tie.

The mayor can veto ordinances subject to an override by a two-thirds majority vote of the council.

[44][45] As of 2024[update], the mayor of Sussex Borough is Republican Robert Holowach, whose term of office ends on December 31, 2027.

[3][46][47][48][49] After the borough council did not vote to select any of the three candidates nominated by the Republican municipal committee, Nicholas R. Holowach was picked by the Republican group and sworn into office in June 2021 to fill the seat expiring in December 2022 that had been held by Walter Cleary III until he resigned from office to move out of the borough.

[49] In January 2020, the borough council selected Linda Masson from a list of three candidates nominated by the Republican municipal committee to fill the seat expiring in December 2021 that was vacated by Edward Meyer when he took office as mayor.

[51] In January 2016, the council appointed Albert Decker from a list three candidates nominated by the Democratic municipal committee to fill the council seat vacated by Katherine Little expiring in December 2017 that became open when she took office as mayor; Decker served on an interim basis until the November 2016 general election, when voters selected a candidate to serve the one year remaining on the term of office.

[52] In January 2015, the borough council selected Mario Poggi from three candidates nominated by the Republican municipal committee to fill the vacant seat of Bruce D. LaBar, who resigned from office earlier that month.

[53] In the November 2015 general election, Frank Dykstra was chosen to fill the balance of the seat expiring in December 2016.

[56][57][58] For the 119th United States Congress, New Jersey's 5th congressional district is represented by Josh Gottheimer (D, Wyckoff).

[61] For the 2024-2025 session, the 24th legislative district of the New Jersey Legislature is represented in the State Senate by Parker Space (R, Wantage Township) and in the General Assembly by Dawn Fantasia (R, Franklin) and Mike Inganamort (R, Chester Township).

At an annual reorganization meeting held in the beginning of January, the board selects a Commissioner Director and Deputy Director from among its members, with day-to-day supervision of the operation of the county delegated to a County Administrator.

[73] Among the borough's 2010 Census population, 53.7% (vs. 65.8% in Sussex County) were registered to vote, including 69.5% of those ages 18 and over (vs. 86.5% countywide).