Leishmaniasis is difficult to control due to clinical and vector diversity associated with the complex life cycle of Leishmania parasites, which are transmitted by sandflies. This study investigated the presence of Leishmania DNA in sandfly vectors, their blood meal sources, and their distribution in relation to environmental and climatic variables in four municipalities in Piauí state, Brazil. Between 2020 and 2022, sandflies were collected, morphologically identified, and analyzed for the presence of parasite DNA and blood meal sources (PCR, sequencing). Climate data were correlated with the density of collected insects. Among the 10,245 specimens collected, Lutzomyia longipalpis (54.87%) and Nyssomyia whitmani (30.41%) were the most abundant in the collection areas. Leishmania braziliensis DNA was detected in Lu. longipalpis, while L. braziliensis and Leishmania infantum DNAs were recovered from Ny. whitmani. Homo sapiens was the main blood meal source (~73%). Vector density was associated with humidity, temperature, and precipitation in Teresina and Pedro II, with significant results for Ny. whitmani. In conclusion, Lu. longipalpis, widely adapted to anthropized environments, can act as a potential vector of the etiological agent of cutaneous leishmaniasis in Teresina and Oeiras. In Pedro II, the detection of L. infantum DNA in Ny. whitmani suggests a possible role of this species in the transmission cycle of visceral leishmaniasis, reinforcing the complex ecoepidemiology of Leishmania spp. in Piauí.