Jamestown Canyon virus (JCV) (Bunyaviridae: Orthobunyavirus) is a mosquito-borne zoonosis belonging to the California serogroup. It has a wide geographic distribution, occurring throughout much of temperate North America. White-tailed deer, Odocoileus virginianus are the principal amplification hosts, and boreal Aedes and Ochlerotatus mosquitoes are the primary vectors. A 10-year study was undertaken to identify potential mosquito vectors in Connecticut, quantify seasonal prevalence rates of infection, and define the geographic distribution of JCV in the state as a function of land use and white-tailed deer populations, which have increased substantially over this period. Jamestown Canyon virus was isolated from 22 mosquito species. Five of them, Ochlerotatus canadensis, Oc. cantator, Anopheles punctipennis, Coquillettidia perturbans, and Oc. abserratus were incriminated as the most likely vectors, based on yearly isolation frequencies and the spatial geographic distribution of infected mosquitoes. Jamestown Canyon virus was isolated from Oc. canadensis more consistently and from a greater range of collection sites than any other species. Frequent virus isolations were also made from Aedes cinereus, Aedes vexans, and Oc. sticticus, and new North American isolation records were established for Anopheles walkeri, Culex restuans, Culiseta morsitans, Oc. sticticus, Oc. taeniorhynchus, and Psorophora ferox. Other species from which JCV was isolated included C. melanura, Oc. aurifer, Oc. communis, Oc. excrucians, Oc. provocans, Oc. sollicitans, Oc. stimulans, Oc. triseriatus, and Oc. trivittatus. Jamestown Canyon virus was widely distributed throughout Connecticut and found to consistently circulate in a diverse array of mosquito vectors. Infected mosquitoes were collected from June through September, and peak infection rates paralleled mosquito abundance from mid-June through mid-July. Infection rates in mosquitoes were consistent from year to year, and overall virus activity was directly related to local mosquito abundance. Infected mosquitoes were equally distributed throughout the state, irrespective of land use, and infection rates were not directly associated with the abundance of white-tailed deer, possibly because of their saturation throughout the region.