The East Asian buprestid Agrilus smaragdifrons Ganglbauer is reported for the first time in the Western Hemisphere. Specimens of this species taken from emerald ash borer (A. planipennis Fairmaire) monitoring traps in New Jersey in 2015–2016 suggest establishment of this metallic wood-boring beetle in the northeastern United States. The earliest known record of A. smaragdifrons in the U.S. is based on a verifiable image found on BugGuide, from a specimen collected in Hudson County, New Jersey in June 2011. Diagnostic information and high-resolution images of the adult male, female, and the male aedeagus are provided to help facilitate the recognition of this adventive buprestid from other North American Agrilus. A summary of information about the host plant (Ailanthus altissima), native distribution, and biology are given, and all known North American records are listed and mapped.