The Katahdin Woods and Waters National Monument Seboeis Unit Vegetation Mapping Project was initiated in the fall of 2019 by a grant through the USGS Natural Resource Preservation Program to classify and map vegetation types of the Seboeis Unit thereby providing resource managers and biological researchers with useful baseline vegetation information. These data are the results of the field effort to collect accuracy assessment data for testing the Katahdin Woods and Waters National Monument Seboeis Unit Vegetation Mapping Project vegetation map. Data collection was assisted by Jennifer Tibbetts, David Rubin, and Tiffany Reese. An accuracy assessment was performed on the draft version of the vegetation map layer. During the summer of 2020, field crews collected data from 107 stratified and randomly selected sites for evaluating the accuracy of the vegetation map layer for those map classes representing U.S. National Vegetation Classification associations. In addition to the ground data, site photos were collected at each accuracy assessment site for a total of 703 ground images. The accuracy assessment field data were then compared to the vegetation map data. Results from the accuracy assessment study show an overall accuracy of 87.6% (kappa index of 87.0%) based on an analysis of data from 105 of the 107 accuracy assessment sites.