Global climate change is leading to large-scale shifts in species' range limits. For example, rising winter temperatures are shifting the abundance and distributions of tropical, cold sensitive plant species towards higher latitudes. Coastal wetlands provide a prime example of such shifts, with tropical mangrove forests expanding into temperate salt marshes as winter warming alleviates past geographic limits set by cold intolerance. These rapid changes are dynamic and challenging to monitor, and uncertainty remains regarding the extent of mangrove expansion near poleward range limits. Here, we synthesized existing datasets and expert knowledge to assess the current (i.e., 2021) distribution of mangroves near dynamic range limits in eastern North America. Each grid cell has a resolution of 0.125 degrees, or approximately 14 x 16 km, within which the presence or absence of mangrove has been independently determined using existing datasets and expert knowledge.