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Culex quinquefasciatus is one of the most important mosquito vectors of arboviruses. Currently, the fastest approach to control disease transmission is the application of synthetic adulticide insecticides. However, in highly populated urban centers the development of insecticide resistance in mosquito populations could impair insecticide efficacy and therefore, disease control. To assess the effect of resistance on vector control, females of Cx. quinquefasciatus collected from six mosquito control operational areas in Harris County, Texas, were treated in field cage tests at three different distances with the pyrethroid Permanone® 31–66 applied at the operational rate. Females were analyzed by sequencing and/or diagnostic PCR using de novo designed primers for detecting the kdr-like mutation in the voltage-gated sodium channel (L982F; TTA to TTT) (house fly kdr canonical mutation L1014F). Females from the Cx. quinquefasciatus susceptible Sebring strain and those from the six operational areas placed at 30.4 m from the treatment source were killed in the tests, while 14% of field-collected mosquitoes survived at 60.8 m, and 35% at 91.2 m from the source. The diagnostic PCR had a with 97.5% accuracy to detect the kdr-like mutation. Pyrethroid resistant mosquitoes carrying the L982F mutation were broadly distributed in Harris County at high frequency. Among mosquitoes analyzed (n = 1,028), the kdr-kdr genotype was prevalent (81.2%), the kdr-s genotype was 18%, and s-s mosquitoes were less than 1% (n = 8). A logistic regression model estimated an equal probability of survival for the genotypes kdr-kdr and kdr-s in all areas analyzed. Altogether, our results point to a high-risk situation for the pyrethroid-based arboviral disease control in Harris County. Author summary: Female Culex quinquefasciatus mosquitoes blood-feed preferentially on birds but also on mammals including humans, to which they may transmit pathogenic arboviruses. To prevent transmission of West Nile and/or other viruses in Harris County, TX, the vector control agency applies mosquito adulticides when arboviruses are detected. Insecticide resistance can hinder mosquito control, increasing the risk of disease transmission. Pyrethroid resistant mosquitoes carry kdr-like mutation(s) in the sodium channel, the pyrethroid target site in the nervous system, that increases survival probability. We investigated frequency and spatial distribution of the kdr-like mutation in Harris County mosquitoes, and how they affect pyrethroid survivorship. We conducted field cage tests with a commercial pyrethroid formulation, and developed molecular tests to detect the kdr-like mutation in females from 6 operational areas. In field tests, almost no mosquito survived at 30.4 m, but 14% and 35% of mosquitoes survived at 60.8 m and 91.2 m. We found 99% of mosquitoes carried at least one kdr-like allele. At the high rate of pyrethroid, the survival probability of mosquitoes carrying one or two kdr-like alleles was not statistically different in the six areas, but survival increased significantly with distance. These results should be considered when analyzing risk of disease transmission. [ABSTRACT FROM AUTHOR]