Royce Brook does not have a definite starting point, as it consists of several bodies of water flowing into it within its 16-square-mile (41 km2) watershed.

However, the website for the Royce Brook Watershed states that it starts at the edge of Sourland Mountain at 40°30′6″N 74°41′48″W / 40.50167°N 74.69667°W / 40.50167; -74.69667.

The origins of the creek's name is unknown, but there is a street that runs parallel to it in Hillsborough called, "Royce Brook Road."

A storm on 15 April 2007 deposited over 7 inches (180 mm) of rain into Royce Brook, which was the most recorded since 1882.

High levels of phosphates have been documented as encouraging too many aquatic plants to grow, using dissolved oxygen from the water (limiting it to the fish), which could be the situation in Royce Brook.