The eastern fox squirrel, native to the eastern and midwestern United States, was recently documented in the Sonoran Desert in the vicinity of Yuma, Arizona, constituting the first state record for this species. We surveyed the people of Yuma to determine when and how the squirrels arrived. The squirrels were first observed in the 1960s, but may have been resident for a longer period. Since the 1960s, squirrels have spread throughout the city limits and extended south similar to 15 km into Somerton, Arizona. How the squirrels arrived is not clear, but must be the result of an introduction, as no nearby populations exist. The persistence of eastern fox squirrels in this unique habitat is due to synanthropic relationships.