New records are presented for Melandryidae Leach, 1815 and Tetratomidae Billberg, 1820 from Arizona in the southwestern United States. Six species of the tetratomid subfamily Eustrophinae Gistel, 1856 were previously confirmed from the state and a single melandryid, Rushia californica (Fall, 1907), was questionably listed from the state. We here confirm the latter record and enumerate seven new state records, bringing the total to 14 species in nine genera. Most notably, we report Microtonus elongatus Champion, 1889 as a new country record for the United States, having been previously known only from the type series from Guatemala and Mexico. An annotated checklist of species is presented including new specimen records examined by us, any available digitized occurrence records, and high-resolution images for all species.