Marksboro is an unincorporated community and census-designated place (CDP)[9] located within Frelinghuysen Township in Warren County, in the U.S. state of New Jersey,[10] that was created as part of the 2010 United States Census,[11][12][13] though settlement and naming of the community date back to before 1760.

[15] Marksboro is named for Colonel Mark Thompson, who built and owned a grist mill on the Paulins Kill here before 1760.

Marksboro had a post office, grist and lumber mill, and a "good local trade".

The 2010 United States census counted 82 people, 30 households, and 25 families in the CDP.

Of all households, 10.0% were made up of individuals and 6.7% had someone living alone who was 65 years of age or older.