Patterns of seasonal variation in the relative abundance of immature Culex mosquitoes in wastewater ponds at dairies located in 2 different regions of peninsular Florida were compared. Culex nigripalpus and Cx. quinquefasciatus were by far the most common mosquitoes collected during the study (99,344 and 106,225 individuals, respectively). Within-station differences in abundance of Cx. nigripalpus and Cx. quinquefasciatus were evident depending upon time of year. There were also between-station differences in the abundances of the 2 species depending upon time of year and station. Environmental and behavioral factors are implicated in some of the observed differences. We discuss mosquito control options for dairy ponds as well as possible impacts of mosquito production from these areas to humans and to animal health and production.