[21] What is now South River was originally formed as the town of Washington within East Brunswick Township on February 23, 1870.

South River was incorporated as an independent borough by an act of the New Jersey Legislature on February 28, 1898, replacing Washington town.

Originally referred to as Washington, the community eventually split away as did Spotswood and Milltown.

[1][2] The borough borders the Middlesex County communities of East Brunswick and Sayreville.

[27][28][29] Unincorporated communities, localities and place names located partially or completely within the borough include Newton Heights, which is situated along the border of South River and East Brunswick.

[38] As of the 2000 United States census[16] there were 15,322 people, 5,606 households, and 3,985 families residing in the borough.

[36][37] Most common ancestries of the population are Polish (18.9%), Italian (14.6%), Irish (13.0%), German (12.5%), Portuguese (9.3%), Russian (4.5%).

[6] The borough form of government used by South River 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.

[43][44] As of 2024[update], the mayor of South River is Republican Peter S. Guindi, whose term of office ends December 31, 2027.

Members of the Borough Council are Council President John Krenzel (R, 2024; appointed to serve an unexpired term), Donna Balazs (R, 2025), Anthony Ciulla (R, 2025), John Frost (R, 2024; appointed to serve an unexpired term), Henry Dziemian (R, 2026) and James Gurchensky (R, 2026).

[3][45][46][47][48] John Frost was appointed in May 2024 to fill the term ending December 2024 that had been held by Jason Oliveira until he resigned from office the previous month.

[49] In January 2014, the borough council selected former councilmember Michael Trenga from among three names nominated by the Republican municipal committee to fill the nearly three years remaining on the vacant seat of John Trzeciak, who cited personal reasons in resigning from office just weeks after taking his seat on the council.

[58] For the 2024-2025 session, the 18th legislative district of the New Jersey Legislature is represented in the State Senate by Patrick J. Diegnan (D, South Plainfield) and in the General Assembly by Robert Karabinchak (D, Edison) and Sterley Stanley (D, East Brunswick).

[60] As of 2025[update], Middlesex County's Commissioners (with party affiliation, term-end year, and residence listed in parentheses) are: Director Ronald G. Rios (D, Carteret, 2027),[61] Deputy Director Shanti Narra (D, North Brunswick, 2027),[62] Claribel A.

[89] The South River Public Schools serve students in pre-kindergarten through twelfth grade.

[102] Route 18 passes just west of the borough, which provides access to the New Jersey Turnpike (Interstate 95).

[103] People who were born in, residents of, or otherwise closely associated with South River include: Rescue 911 (Season 3, Episode 25) features a segment about a Good Samaritan who assisted in the rescue of an occupant from an apartment fire on January 8, 1991, at the Emess Apartments (now known as Deer Creek Village).