Substantial funding is being allocated to new land protection and access to protected open space for marginalized communities is a crucial concern. Using New England as a study area, we show striking disparities in the distribution of protected open space across multiple dimensions of social marginalization. Using a quartile-based approach within states, we find that communities in the lowest income quartile have just 52% as much nearby protected land as those in the most affluent quartile. Similarly, communities with the highest proportions of people of color have just 47% as much protected land as those in the lowest quartile. These disparities persist across both public and private protected land, within urban, exurban and rural communities, for different sized buffers around communities, and across time. To help address these disparities in future conservation plans, we develop a screening tool to identify and map communities with high social marginalization and low nearby protected open space within each state. We then show that areas prioritized according to these environmental justice criteria are substantially different from areas prioritized according to conventional conservation criteria. This demonstrates how incorporating environmental justice criteria in conservation prioritization processes could shift patterns of future land protection. Our work provides methods that can be used broadly across regions to inform conservation efforts.