The film was shot in Los Angeles. This is not only due to convenience for filming, but also a kind of homage to detective noirs. The film is a family parody of detective movies, or perhaps not even a parody, but a collection of some generalization of clichés. These films were mostly shot in Los Angeles and also told stories about this city. Therefore, the filming location was obvious. 

Filming Locations:

Tunnel to Toontown

In the Movie

The scene where Detective Eddie Valiant approaches the tunnel leading to Toontown, chasing a white car. But he stops and gets out of the car with a weapon, as he hesitates to enter the cartoon city. He drinks whiskey, picks up a drawn gun, and continues on his way.

In Reality

The scene was filmed at the entrance to the tunnel in Griffith Park, a large park in the center of Los Angeles. Most likely, this location does not carry any secret meaning, but is simply convenient for filming and has few people in the evening. For the film, the arch was decorated with stucco to make the entrance to the cartoon city look more festive.