Actinopus Perty, 1833 is characterized and redescribed, including 80 species occurring from Panama to Argentina. Eighteen previously known species are redescribed: A. rufipes (Lucas, 1834); A. longipalpis C. L. Koch, 1842; A. nattereri (Doleschall, 1871); A. crassipes (Keyserling, 1891); A. robustus (O. Pickard-Cambridge, 1892); A. wallacei F. O. P.-Cambridge, 1896; A. princeps Chamberlin, 1917; A. xenus Chamberlin, 1917; A. fractus Mello-Leitão, 1920; A. paranensis Mello-Leitão, 1920; A. pusillus Mello-Leitão, 1920; A. dubiomaculatus Mello-Leitão, 1923; A. trinotatus Mello-Leitão, 1938; A. cucutaensis Mello-Leitão, 1941; A. echinus Mello-Leitão, 1949; A. clavero Ríos-Tamayo & Goloboff, 2018; A. gerschiapelliarum Ríos-Tamayo & Goloboff, 2018; and A. palmar Ríos-Tamayo & Goloboff, 2018. Additionally, A. tarsalis Perty, 1833, the type species, A. insignis (Holmberg, 1881) and other 18 species recently described species from Argentina and Bolivia, are re-evaluated. Forty-two new species are described: Actinopus castelo sp. nov., A. apalai sp. nov., A. mairinquensis sp. nov., A. obidos sp. nov., A. buritiensis sp. nov., A. pinhao sp. nov., A. ducke sp. nov., A. hirsutus sp. nov., A. jaboticatubas sp. nov., A. confusus sp. nov., A. pampulha sp. nov., A. candango sp. nov., A. paraitinga sp. nov., A. cornelli sp. nov., A. vilhena sp. nov., A. harveyi sp. nov., A. itapitocai sp. nov., A. ipioca sp. nov., A. itaqui sp. nov., A. xingu sp. nov., A. mesa sp. nov., A. caxiuana sp. nov., A. utinga sp. nov., A. emas sp. nov., A. bocaina sp. nov., A. osbournei sp. nov., A. dioi sp. nov., A. tutu sp. nov., A. azaghal sp. nov., A. itacolomi sp. nov., A. parafundulus sp. nov., A. urucui sp. nov., A. reznori sp. nov., A. anselmoi sp. nov., A. guajara sp. nov., A. apiacas sp. nov., A. jamari sp. nov. from Brazil; A. laventana sp. nov. from Argentina and Uruguay; A. lomalinda sp. nov. from British Guiana and Colombia; A. concinnus sp. nov. from Venezuela and Brazil; A. pindapoy sp. nov. from Argentina; A. panguana sp. nov. from Peru. The females of A. dubiomaculatus and A. cucutaensis and the males of A. nattereri are described for the first time. New records are presented for A. clavero; A.crassipes; A. dubiomaculatus; A. fractus; A. gerschiapelliarum; A. nattereri; A. palmar; A. paranensis; A. princeps, A. pusillus, A. robustus and A. wallacei. Ten old species names are herein considered species inquirendae: A. caraiba (Simon, 1889); A. harti Pocock, 1895; A. liodon (Ausserer, 1875); A. nigripes (Lucas, 1834); A. pertyi Lucas, 1843; A. piceus (Ausserer, 1871); A. rojasi (Simon, 1889); A. rufibarbis Mello-Leitão, 1930; A. scalops (Simon, 1889) and A. valencianus (Simon, 1889). Most species presently recognized were included in 11 informal groups based mainly on male palpal characters. A key for these groups plus three species, not included in any group, but known from males, is presented.