Ecological analysis was used to evaluate over 2 yr of adult mosquito surveillance data from Citrus County, Florida. The analysis was intended to demonstrate a systematic approach to make better use of the abundance of surveillance data as a prerequisite to predict future mosquito population trends. Twenty-eight mosquito species (157,600 individuals) were collected using a modified New Jersey light trap. Analysis of species dominance index revealed that the seven most dominant species comprised 84% of the total individuals captured. Three culicine mosquitoes, Culex quinquefasciatus, Cx. nigripalpus, and Cx. erraticus, showed recurring seasonal abundance peaks in July and August, while two anopheline species, Anopheles crucians and An. atropos, showed interannual abundance variability. The population of the salt-marsh mosquito, Ochlerotatus taeniorhynchus, consistently peaked in June and July, while that of Oc. infirmatus peaked in September and July of 1999 and 2000, respectively. With 66% Oc. taeniorhynchus, the Ozello site had the highest aggregation index (0.4975) of all the trap sites in the county. Adult mosquitoes exhibited the highest diversity (index = 2.3476) at a mixed salt-marsh and freshwater site (Homosassa). A cluster analysis provided a systematic way to gauge both similarities and dissimilarities of sites and divided the 14 trap sites into 7 basic groups. For districts that have a large number of trap sites, results of cluster analysis might be used to streamline the adult mosquito surveillance program by combining or relocating traps with very similar mosquito collections.