Fort Union Trading Post National Historic Site (FOUS) protects 444 acres of northern mixedgrass prairie and riparian forests. The Northern Great Plains Inventory & Monitoring Network surveyed 6 long-term monitoring plots in FOUS in 2012 as part of an effort to better understand the condition of plant communities in the park. We measured plant diversity and cover, looked for the presence of exotic species that are of concern to park management, and evaluated the amount of human and natural disturbance at all plots. This effort was the second year in a multiple-year venture to document the current status and long-term trends in plant communities in FOUS. At the end of five years, there will be an in-depth report describing the status of the plant community. In this report, we provide a simple summary of our results from sampling in 2012.