Abiotic and biotic variables strongly influence morphological variation in wildlife, but there is disagreement on the relative importance of various factors. Primary competing hypotheses regarding drivers of interpopulation animal morphology include those related to heat regulation and those related to forage availability. Despite data to support both hypotheses in various systems, few have considered fine-scale forage availability data across a large geographic area. White-tailed deer (Odocoileus virginianus) body and antler size vary widely across their geographic distribution, with larger deer often associated with landscapes providing large amounts of high-quality forage. However, there is limited information on the influence of temperature, landscape, and site-specific forage availability on deer morphology across a wide geographic area. We collected body mass, antler size, and site-specific growing-season forage availability from 35 locations across 21 eastern U.S. states. Average female body mass increased by 1.4 kg for every 1˚C decrease in average annual temperature and increased by 1.6 kg for every 10% increase in landscape crop coverage. Mature male antler size also correlated with temperature and crop coverage, with antler size increasing 4.9 cm for every 1˚C decrease in average annual temperature and increasing 7.1 cm for every 10% increase in landscape crop coverage. After controlling for landscape effects, adult female mass was correlated with site-specific nutritional carrying capacity based on a 0.3% phosphorus constraint (P NCC), with average female body mass increasing 0.15 kg for every 1 deer day/ha increase in P NCC. Male antler size was marginally correlated with P NCC as well, with antler size increasing 0.7 cm for every 1 deer day/ha increase in P NCC. Our results support the Resource Rule at the local scale, but temperature and landscape factors contribute to interpopulation variation in morphology across broad spatial scales.