Japanese barberry can be found in most northeastern and Great Lakes states of the United States. A current map of its distribution can be found at the Early Detection and Distribution Mapping System (EDDmapS). In recent years, "Berberis thunbergii" has been recognized as an invasive species in many parts of the eastern United States. The Plant Conservation Alliance's Alien Plant Working Group lists it among its "Least Wanted". Japanese barberry is prohibited from being a seed contaminant in Michigan and banned from sale in Massachusetts. This species is ranked (Very High) on the New York State Threat Assessment scale.