Non-native European earthworms are invading hardwood forests in the Chippewa National Forest, MN. We applied a model using historic O-horizon soil thickness to classify 41 hardwood sites in the Chippewa National Forest as “long-term wormed” (wormed during the 1989-1996 and 2017 sampling period), “short-term wormed” (unwormed during the 1989-1996 sampling period and wormed in the 2017 sampling period), or “unwormed” (unwormed during the 1989-1996 and 2017 sampling period). We found that graminoids, especially Carex pensylvanica , had the greatest abundance in sites that had been wormed for over two decades. The families with the greatest negative change in percent cover after over two decades of earthworm invasion were Asteraceae, Violaceae, and Sapindaceae (specifically Acer species). Across all diversity metrics measured, long-term wormed sites had the lowest understory plant species diversity, short-term wormed sites had intermediate diversity, and unwormed sites exhibited the highest diversity. Long-term wormed sites had the lowest species richness at both small and large scales (1 to 1024m 2 ). The greatest within-group compositional dissimilarity occurred at sites that had been wormed for over two decades, indicating that compositional changes in plant communities are still occurring more than two decades since invasion. Sites that had been wormed for over two decades did not appear to have reached a compositionally similar end-state “wormed” community type. If results of this study are indicative of future trends as earthworms become established, it can be expected that understory diversity will decrease as hardwood forest stands become wormed over time.