Nauvoo v. Ritter was a United States Supreme Court case that dealt with the issue of whether a city could be held liable for damages caused by a mob. The case arose when a mob of citizens from the city of Nauvoo, Illinois, destroyed the property of a man named Ritter. Ritter sued the city of Nauvoo for damages, claiming that the city had failed to protect him from the mob. The Supreme Court held that the city of Nauvoo could not be held liable for the damages caused by the mob. The Court reasoned that the city had no legal duty to protect Ritter from the mob, and that the mob was not acting on behalf of the city. The Court also noted that the city had taken steps to try to prevent the mob from forming, and that the city had not authorized or encouraged the mob's actions. The Court's decision in Nauvoo v. Ritter established that cities cannot be held liable for damages caused by mobs, unless the city had a legal duty to protect the victim or had authorized or encouraged the mob's actions. This decision has been cited in numerous subsequent cases involving mob violence and municipal liability.

In the case of Nauvoo v. Ritter, the Supreme Court was asked to decide whether a city ordinance passed by the City Council of Nauvoo, Illinois in 1845 could be enforced against non-residents who had purchased property within its limits. The majority opinion held that it could not because such an ordinance would violate both state and federal constitutional provisions protecting citizens from unreasonable searches and seizures as well as due process rights. However, Justice Field dissented on this point arguing that while he agreed with the majority's conclusion regarding state law violations, he disagreed with their interpretation of federal law which did not necessarily prohibit local ordinances like those at issue here. He further argued that even if they were found to be unconstitutional under federal law, it should still be up to each individual state court to make such determinations rather than for the Supreme Court itself since states have traditionally been given wide latitude when interpreting their own laws.