Diversifying crop systems represents a promising pathway to improved climate resilience in agriculture. After a century of radical crop system simplification, understanding processes of crop system diversification requires accounting for multiple interlinked factors and their contexts. This article suggests that the theoretical tools of land systems science offer a particularly useful approach for understanding processes of crop diversification at the meso-level. Results are presented from a mixed-methods project that used national datasets to identify agriculturally important counties in the United States whose cropping systems trended strongly towards either simplification or diversification between 2008 and 2020, then used in-depth interviews in two neighboring counties with opposite diversification trajectories to identify explanatory factors. Actors in both counties employed similar logic and values vis-à-vis markets, equipment, labor, and relationships, but were embedded within distinct ecological and political contexts that strongly influenced their diversification trajectories. We argue that crop diversification can be more productively understood as a meso-level process of land use change than a function of individual decision-making. Land systems approaches’ attention to social and biophysical dimensions, historical perspectives, and emphasis on embedding actors within socio-environmental contexts offer benefits for future work on processes of crop diversification.