The mosquito species Aedes aegypti (Linneaus) is the vector of multiple arboviruses, including dengue, Chikungunya, Zika, and yellow fever. Risk of infections associated with these arboviruses continues to expand as the geographical range of Ae. aegypti extends into temperate regions. Although Ae. aegypti is abundant along the U.S.–Mexico border, the ecology of this mosquito species in this temperate/subtropical desert is not well understood. Our study objective was to estimate the seasonal population density in 2 urban communities: Sparks, El Paso, Texas and Anapra, Ciudad Juárez, Chihuahua, Mexico. Estimates of the population density of adult Ae. aegypti were obtained by month (June to December) and across years (2016 to 2018) using gravid traps. Mosquitoes were collected inside and outside a total of 108 and 101 participating homes in Sparks and Anapra, respectively. We determined multiple environmental and climatic factors influencing annual population trends. Generally, an increase in the abundance of Ae. aegypti was associated with an increase in precipitation, moderate temperatures, and high humidity, while months with temperatures below 4.4°C led to near absence of adults. Across months, we found low densities of Ae. aegypti during June and July, followed by near 100-fold increases in abundance from August to October before rapidly decreasing to near zero in subsequent cold season months. Our study sheds light on population dynamics and response variables at the leading edge of Ae. aegypti range, which require the development of targeted vector control measures for this mosquito species in this and other regions.