We describe three new species of Trigonospila Pokorny (Tachinidae: Blondeliini) from Area de Conservación Guanacaste (ACG), northwestern Costa Rica. All were reared from ­various species of ACG caterpillars during an ongoing inventory of caterpillars, their food plants and their parasitoids in dry forest, rain forest and cloud forest. By coupling morphology, photographic documentation, life history and molecular data, we provide a clear and concise description of each species. All species published as new, are known to be previously undescribed as a result of careful study of the genus by DMW. This study builds on the current knowledge of the genus by adding three new species to the current 7 described in the New World. Trigonospila edwinbermudezi sp. n., Trigonospila uniformis sp. n., and Trigonospila josemariamoragai sp. n. are all authored and described as new by Fleming and Wood, with a key to their identification. The authors also offer a new record and description of the previously unknown male of Trigonospila panamensis (Townsend), reared from ACG caterpillars.