Soil carbon dioxide efflux is impacted by urbanization but few studies have directly examined it in contrasting human‐dominated land uses. We tested the hypothesis that soil carbon dioxide efflux would be greater in residential lawns than corn fields in Lancaster County, PA, by measuring soil carbon dioxide efflux, soil temperature, and soil moisture once a week for 10 wk in the fall of 2011. Soil carbon dioxide efflux occurring in residential lawns was significantly higher (F 1,6 = 7.46, p = 0.034) than the levels in corn ( Zea mays L.) fields for the duration of the study. Soil carbon dioxide efflux significantly decreased over time in both land‐use types (F 9,54 = 37.34, p < 0.001). Soil temperature, soil moisture, and land‐use type significantly contributed to the efflux ( R 2 = 0.744, F 3,76 = 73.443, p < 0.001). Higher soil temperatures in residential lawns were attributed to an urban heat island. Our results suggest converting agricultural land to residential developments could increase soil carbon dioxide release per unit area of soil, especially if urbanization increases local soil temperatures.