Previous work on Bartram’s round-winged katydid, Amblycorypha bartrami Walker, found inconsistencies in song variation across the species’ range. Individuals of purported populations of A. bartrami from sandhills across the southeastern US were collected, recorded, and their genes were sequenced to better understand their population structure and evolution. Significant differences in songs, morphology, and genetics were found among populations from Alabama (AL), Georgia (GA), North Carolina (NC), and South Carolina (SC), and they differed from those of individuals collected from the type locality in Florida (FL). Males from all populations produced songs composed of a series of similar syllables, but they differed in the rates at which syllables were produced as a function of temperature. At temperatures of 25°C, the calling songs of males from populations in northern AL and GA were found to have the highest syllable rates, those from SC had the lowest rates, and those from NC were found to produce songs with doublet syllables at rates that were intermediate between those of males from FL and those of AL and GA. These song differences formed the basis for cluster analyses and principal component analyses, which showed significant clustering and differences in song spectra and morphology among the song morphs. A Bayesian multi-locus, multi-species coalescent analysis found significant divergences from a panmictic population for the song morphs. Populations from GA and AL are closely related to those of A. bartrami in FL, whereas populations from NC and SC are closely related to each other and differ from the other three. Large river systems may have been important in isolating these populations of flightless katydids. Based on the results of our analyses of songs, morphology, and genetics, three new species of round-winged katydids from the southeastern coastal plain and piedmont are described.