This study examined the distribution of the freshwater red algal species, Sheathia involuta, from the southwestern United States and northern Mexico. Due to multiple difficulties associated with using morphological characteristics, identifications were based solely upon molecular analysis using genetic markers to identify specimens. Tissue samples were collected from eight rivers systems from 2020 to 2022 and subjected to PCR amplification to obtain DNA sequence data from the COI barcode region and the rbcL gene fragment. Results confirm positive identifications of Shaethia involuta. This study extends the currently known range of S. involuta into western Texas, southern New Mexico as well as the states of Coahuila and Chihuahua in northern Mexico.