The area experiences a humid subtropical climate with warm summers and cold winters. The borough lies in the upper Rockaway River watershed, and its hydrology constituents include the Rockaway River, Indian Lake, and Cedar Lake. Outdoor enthusiasts can enjoy several recreational opportunities in Denville, including hiking and biking trails, fishing, boating, and swimming at the many lakes throughout the area. Tourists can also visit the nearby Tourne County Park, which offers hiking trails, bird-watching opportunities, and scenic views of the New York City skyline.
Denville receives approximately 1332mm of rain per year, with humidity levels near 81% and air temperatures averaging around 10°C. Denville has a plant hardyness factor of 6, meaning plants and agriculture in this region thrive during a short period during spring and early summer. Most plants will die off during the colder winter months.