This paper treats the genus Phaulotettix Scudder, 1897, which previously included only three species. In this work we describe 12 new species: P. adibilis n. sp., P. opimus n. sp., P. altissimus n. sp., P. ablusus n. sp., P. adiaphoros n. sp., P. ambrosius n. sp., P. arcadius n. sp., P. flaccidus n. sp., P. affinis n. sp., P. adynatos n. sp., P. nimius n. sp. and P. jocundus n. sp. Species separation is based on male cerci and internal genitalia. The members of this group are distributed mostly in northeastern Mexico: Cohauila, Nuevo León, Tamaulipas, San Luis Potosí, Hidalgo and north Veracruz. Two species, P. compressas Scudder, 1897 and P. eurycercus Hebard, 1918, extend their distribution into Texas, USA. Many of the species treated here overlap geographically, and many occur sympatrically. We also provide a brief discussion of the geography of northeastern Mexico.