Knowledge about mosquito species diversity at tropical montane cloud forests (TMCFs) in Mesoamerica is scarce. Here, we present data on mosquito species richness from samples biweekly collected, from January to December 2017, in ovitraps installed in aTMCF patch at Vázquez de Coronado County, Costa Rica. Ovitraps were placed at 2.25, 1.50 and 0.75 m at 16 sampling points. During the study period we measured relative humidity and air temperature at each sampling point, and water temperature, volume and pH in each ovitrap. We collected a total of 431 mosquito larvae belonging to five taxonomic units, one identified to the genus level and four to the species level. The most common mosquito species was Culex bihaicolus Dyar & Nuñez Tovar (Diptera: Culicidae), which accounted for nearly 80% (n = 344) of the collected mosquitoes. Culex nigripalpus Theobald (Diptera: Culicidae) was the only medically important species we found and it was collected both in the dry (January to March) and rainy season (April to December). Over 95% (n = 411) of the mosquitoes were collected during the rainy season and 60% (n = 257) at 0.75 m. Among the environmental variables that we measured, only water volume and pH were significantly (P < 0.05) different between the dry and rainy season, the former increasing and the later decreasing during the rainy season. These results suggest that rainfall plays a major role regulating the phenology of the sampled mosquito species and highlight the need to screen for pathogens in Cx. nigripalpus at the study area.