This data release consists of mosquito and spatial coordinate data collected along the Halepaʻakai Stream drainage in the Alakaʻi Wilderness Preserve on the island of Kauaʻi from late 2018 to early 2019. These data reflect the first extensive, systematic surveys of adult and larval southern house mosquitoes, Culex quinquefasciatus, in breeding habitat for the critically endangered ʻakikiki and ʻakekeʻe. Several nights of mosquito trapping were also conducted at Hanalei National Wildlife Refuge. C. quinquefasciatus is the primary vector of avian malaria in Hawaii, a disease that has been implicated in the decline of endemic forest birds across the state. The main objectives of the study were to: (1) collect adult mosquito count data to understand population dynamics, seasonality, and movement of C. quinquefasciatus along streams and ridges from 20–1380 m asl; (2) conduct standard stream surveys along 800 m of Halepaʻakai stream to determine larval habitat availability and occurrence of mosquito larvae; (3) collect mosquito larvae count data, characterize larval mosquito pools, and assess larval habitat availability along opportunistically sampled sections of Halepaʻakai, Māmaki, Halehaha, and Waiʻalae streams, as well as pools along trails; (4) dissect mosquitoes to assess avian malaria infection status; and (5) collect GPS coordinate data for adult traps, camps, and pools. Each of these components has a single csv file associated with it, as well as metadata and process steps. This study was conducted by U.S. Geological Survey, Pacific Island Ecosystems Research Center, Kauaʻi Forest Bird Recovery Project, and Hanalei National Wildlife Refuge. The following files are included in this data release: 1) Kauai2018_AdultMosquitoCaptures.csv 2) Kauai2018_DipSurveys.csv 3) Kauai2018_LarvalCounts.csv 4) Kauai2018_MosquitoDissections.csv 5) Kauai2018_GPSCoordinates.csv