Local and regional land use changes, such as the expansion of cellulosic biofuels, and population density of deer can affect the health and body mass of white-tailed deer (Odocoileus virginianus). We collected hunter-harvest data for 1,731 white-tailed deer from DeSoto National Wildlife Refuge (DNWR) in eastern Nebraska and western Iowa, USA from 2003-2010. We used linear mixed-effects models and information theoretic methods to estimate effects of density of deer and proportion of total landcover area converted from cropland to cool- or warm-season grassland on body mass of white-tailed deer. Density of deer at DNWR ranged from 36.5 deer/km2-50.6 deer/km2 and the proportion of landcover at DNWR that remained cropland each year ranged from 14.9%-23.2%. Body mass was inversely related to population density (−1.4 kg/5.5 deer/km2) and proportion of cropland (−1.3 kg/3.1% conversion of total land area from cropland to grassland). We used auxiliary harvest data collected at Boyer Chute National Wildlife Refuge (BCNWR) to validate our models and found our models performed well. We estimate densities of deer must be reduced by 1.7 (SE=0.6) deer/km2 for every 1% change in total landcover from cropland to grassland in order for deer to maintain body mass. Our results indicate increased harvest of deer, resulting in a reduction in population density, will offset negative effects a decline in the amount of available cropland could have on the body mass and health of white-tailed deer.