Thonalmus Bourgeois, 1883 is one of the most charismatic and widely recognizable net-winged beetle genera in the New World, currently composed of 13 valid species. The absence of an updated identification key for the species, lack of accurate species delimitations, erroneous information regarding the distribution of some of the species and the inexistence of a taxonomic revision of the genus make the identification of Thonalmus at the species level an impossible task. To address these problems and to expand our knowledge of the group, a large-scale study of Thonalmus has been undertaken. Thonalmus was revised and type specimens of all described species were examined. Detailed redescriptions and rediagnoses are presented for the genus and the already-described species, followed by the illustration of diagnostic characters, the development of a taxonomic identification key, distribution maps, and updates in the nomenclature of the group. Seven new species are described: Thonalmus abejaensis Ferreira and Ivie, new species, Thonalmus centralis Ferreira and Ivie, new species, Thonalmus darlingtoni Ferreira and Ivie, new species, Thonalmus guerreroi Ferreira and Ivie, new species, Thonalmus humeralis Ferreira and Ivie, new species, and Thonalmus thomasi Ferreira and Ivie, new species from Hispaniola and Thonalmus milleri Ferreira and Ivie, new species from Puerto Rico and Hispaniola. Thonalmus bahamae Leng and Mutchler, 1922 is proposed as a new junior synonym of Thonalmus aulicus (Jacquelin du Val, 1857) and Thonalmus chevrolati Bourgeois, 1901 is proposed as a new junior synonym of Thonalmus bicolor (Linnaeus, 1763). The confusion regarding the distribution of T. bicolor is clarified: true T. bicolor is only known to occur in Hispaniola, and the species with a triangular scutellar shield, commonly found in Jamaica, is identified as Thonalmus militaris (Dalman, 1817), and its status as a valid species is reinstated; with these reforms and descriptions, the total number of valid species of Thonalmus is raised to 19. We also provide species-level phylogenetic hypotheses (morphology, molecular, and total-evidence based), as well as biogeographical dispersal patterns hypotheses, a time-calibrated phylogeny, and a character-state reconstruction for the species of Thonalmus. The Thonalmus species-level phylogenetic hypotheses were proposed based on 77 morphological characters and four molecular marker (18S rRNA, D2 region of 28S rRNA, cox1–3′ mtDNA and fragments of rrnL) datasets using Bayesian inference (BI), maximum likelihood (ML), and maximum parsimony (MP) approaches. In all our analyses, Thonalmus was recovered as a monophyletic group with high to moderate support levels, but support levels for the clades within the genus varied according to the reconstruction method and sources of data. Our ancestral area reconstruction provided relatively high support for the hypothetical ancestral area of all Thonalmus being Hispaniola and/or Hispaniola and Cuba, and our time-calibrated phylogenies recovered mean node ages for Thonalmus ranging from 48.85 to 68.34 Ma.