The nine species of Sassacus Peckham & Peckham 1895 known from Canada, the United States, and Mexico are described. The genus as defined here includes: Sassacus papenhoei Peckham & Peckham 1895, Sassacus paiutus (Gertsch 1934), Sassacus samalayucae Richman (new species), Sassacus cyaneus (Hentz 1846), Sassacus alboguttatus (F.O. Pickard–Cambridge 1901), Sassacus vitis (Cockerell 1894), Sassacus aztecus Richman (new species), Sassacus barbipes Peckham & Peckham 1888, and Sassacus lirios Richman (new species). Agassa Simon 1901 is synonymized with Sassacus. “Typical” (beetle-like) and more “normal” (spider-like) Sassacus range from Southern British Columbia south into Central America. The Sassacus arcuatus group, which is much more extensive in South America, possibly belongs to its own genus and is not treated beyond one species described here from Mexico.