Located in northwestern Warren County along the Delaware River, Knowlton Township encompasses 25 square miles. Included in this municipality are the hamlets of Columbia, Delaware, Hainsburg, Knowlton, Mt. Pleasant, Polkville, and Ramseysburg. Three major roadways, Interstate 80 and Routes 46 and 94, pass through the Township. Active railroads also pass from east to west through the central and the southwestern portions of Knowlton.

In spite of this large number of major transportation routes, Knowlton remains mostly rural. The Township boasts a large amount of permanent open space and good public support for continuing its preservation goals.

Knowlton's rich soils are currently in cropland, and small livestock farms are also common throughout the municipality. The more rugged areas in the northern portion of the Township are dominated by hardwood forests. Commercial and industrial development is mainly concentrated along the major highway corridors. In recent years, residential subdivisions have begun to spread throughout Knowlton. There is no sewer service, and so developments are served by individual septic systems.

The northernmost portion of Knowlton belongs to the Delaware Water Gap National Recreation Area and Worthington State Park. The Paulinskill Valley Trail, 180 a Rails to Trails project maintained by the State Parks Department, passes through the Township and is accessible at several points. Knowlton's recreational areas also include numerous public access areas on the Delaware River, several private campgrounds, and Delaware Lake.

The Township falls within five watersheds or sub-watersheds, including the Stonybrook, the Paulinskill, Delawanna Creek, the Pequest, and the Delaware. The Paulinskill River passes through the center of Knowlton on its way to the Delaware. Many of the Township's streams are classified as Trout Production Waters by the New Jersey Department of Environmental Protection, indicating their high water quality and granting them maximum protection under the State's regulations.