[3] According to the book Historical Sites of Warren County, the township was named for Theodorus Jacobus Frelinghuysen, a minister and theologian of the Dutch Reformed Church who came to New Jersey in 1720.

[21] Theodorus was the grandfather of Theodore Frelinghuysen, the noted statesman, educator and running mate of presidential candidate Henry Clay on the Whig Party ticket in the 1844 election, who is also credited as the inspiration for the township's name.

[25][26][27] Other unincorporated communities, localities and place names located partially or completely within the township include Ebenezer, Glovers Pond, Kerrs Corners, Shiloh, Southtown and Yellow Frame.

[29][30] The township's economic data (as is all of Warren County) is calculated by the US Census Bureau as part of the Allentown-Bethlehem-Easton, PA-NJ Metropolitan Statistical Area.

[41] The 2010 United States census counted 2,230 people, 760 households, and 615 families in the township.

Of all households, 13.6% were made up of individuals and 5.1% had someone living alone who was 65 years of age or older.

[42] As of the 2000 United States census,[15] there were 2,083 people, 722 households, and 578 families residing in the township.

[4][45][46][47][48] In January 2022, Robert Stack was sworn in to fill the seat expiring in December 2022 that had been held by Frank D. Desiderio Jr. until his resignation the previous month.

[52] For the 119th United States Congress, New Jersey's 7th congressional district is represented by Thomas Kean Jr. (R, Westfield).

[54] For the 2024-2025 session, the 23rd legislative district of the New Jersey Legislature is represented in the State Senate by Doug Steinhardt (R, Lopatcong Township) and in the General Assembly by John DiMaio (R, Hackettstown) and Erik Peterson (R, Franklin Township).

[59][60] Constitutional officers of Warren County are: Clerk Holly Mackey (R, Alpha; 2027),[61][62] Sheriff James McDonald Sr. (R, Phillipsburg; 2025)[63][64] and Surrogate Michael J. Doherty (R, Washington; 2025).

[68] Among the township's 2010 Census population, 71.0% (vs. 62.3% in Warren County) were registered to vote, including 90.6% of those ages 18 and over (vs. 81.5% countywide).

[87] Students from the township and from all of Warren County are eligible to attend Ridge and Valley Charter School in the township (for grades K–8, with Frelinghuysen residents among those receiving admissions preference)[88] or Warren County Technical School in Washington borough (for 9–12),[89] with special education services provided by local districts supplemented throughout the county by the Warren County Special Services School District in Oxford Township (for PreK–12).

CR 519 is the main county road that passes through roughly from the southwest to the northeast.

People who were born in, residents of, or otherwise closely associated with Frelinghuysen Township include: