Elbert Little’s tree species range maps and Forest Inventory and Analysis (FIA) are two important data sources used to create historic and current tree species distributions. Yet, explicit comparisons do not exist between the two data sets. We developed a statistical procedure to compare forty-seven tree species of expert-drawn Little’s range maps to point-to-grid maps of FIA in terms of their northern and southern range extent and range porosity. First, we computed varying percentiles of species occurrence for northern and southern ranges using empirical cumulative distribution functions. Then, we evaluated distributional differences between the maps using the nonparametric two-sample Kolmogorov–Smirnov and Anderson–Darling statistics and compared these results to the conventional Jaccard dissimilarity index. Our methods found map dissimilarities near northern and southern range extents and range porosity that conventional methods failed to detect. We also found that map disparity is related to an untraceable source of errors related to abundance of species for Little’s range map and, to a lesser extent, forest area changes over the forty years. We conclude that Little’s range map has an overall tendency to draw generous range extents with little emphasis on range porosity for abundant species compared to FIA.