Factual error: Mel and Goldie board a ferry. A visible sign states 'Detroit-Racine Ferry'. Detroit is on the east side of the state of Michigan but Racine, Wisconsin is west of Michigan, across Lake Michigan. The only water route to get from Detroit to Racine would be to circumnavigate the entire state of Michigan.
Factual error: Mel and Goldie ride through Chinatown in Racine WI. Racine does not have a Chinatown and the city is nowhere near as large as they represent it to be.
Factual error: When Mel's character first calls the Witness Relocation Program after Goldie's character sees him at the gas station he talks to his new case worker and tells him that he does not remember him. The case worker then says "You know all us FBI Guys sound the same". The FBI does not run the Witness Relocation Program. It is run by the U.S. Marshals, a completely different organization.
Factual error: The 'zoo' where the final climax of the movie takes place is built in perfect movie logic; it is full of deadly hazards (unmarked, small innocuous looking pond filled with piranhas, suspension bridge that collapses when a 100 pound woman steps on it, etc) arranged in ways that either normal visitors would not be able to even notice (making them pointless in context) or that would cause horrible accidents.