Gnamptogenys triangularis (Mayr) is a predatory ant that feeds primarily on millipedes. This species has an enormous native range in South and Central America that extends from subtropical Argentina (38.1°S) to tropical Costa Rica (10.4°N). The earliest known records of G. triangularis outside its native range were from Florida beginning in 1985, with subsequent published records from Alabama (1996–) and Mississippi (2002–). Here, we present new records of G. triangularis documenting further expansion of populations in the southeastern US, including first published site records from Texas (2013–), Louisiana (2019–), and South Carolina (2019–). In the southeastern US, G. triangularis occurs in a wide range of habitats, from relatively intact forest to highly disturbed urban sites. Its northernmost site records are from South Carolina (34.1°N), but based on its South American range, G. triangularis may have the potential to spread further north. Gnamptogenys triangularis readily consumes the greenhouse millipede, Oxidus gracilis (Koch), a cosmopolitan species originally from Asia, which is now very common in disturbed environments of the southeastern US, so potential prey for G. triangularis may be plentiful throughout this region.