Mad River can refer to one of several rivers in North America

The Mad River flows nearly 60 mi (97 km) from Logan County, Ohio, to downtown Dayton, Ohio, where it meets the Great Miami River. The river flows southwest from its source near Campbell Hill through West Liberty, Ohio, along U.S. Route 68 west of Urbana, Ohio, past Springfield, Ohio where it meets up with Buck Creek, then along State Route 4 into Dayton.

The Mad River is a river in upper Northern California. It flows for 95 miles in a roughly northwest direction through Trinity County and then Humboldt County and drains a 497 square mile-watershed into the Pacific Ocean near Arcata-Eureka Airport in McKinleyville. The river's headwaters are in the Coast Range near South Kelsey Ridge.