Thunderhill Raceway Park is a motorsports complex located 7 mi (11 km) west of Willows, California, United States, in the Sacramento Valley.

It is the venue for the longest automobile race in the United States, the 25 Hours of Thunderhill, held annually during the first weekend in December.

Following the closure of the Baylands Raceway in Fremont, CA, the purchase of the land and construction of Thunderhill was funded by the San Francisco Region Sports Car Club of America.

In late 1997, the track was expanded to its present-day 2.866 mi (4.612 km) configuration, adding six new turns, a bypass for the "cyclone" corner, and additional paved paddock space.

At the time of construction, this was the longest racetrack in California, and it gained the nickname "Thunderschleife" as a nod to the Nurburgring Nordschleife.