Interseeding annual crops into existing alfalfa (Medicago sativa L.) stands is gaining interest, and one reason may be that alfalfa lowers nitrogen requirements for subsequent crops. However, little is known about the legacy impact of this practice on subsequent corn (Zea mays L.) production. An experiment involving interseeding annual cool‐season crops into alfalfa was conducted between 2017 and 2021, which serendipitously allowed us to evaluate the legacy impact of this practice on subsequent corn grain production. This follow‐up study compared corn grain yield and quality of corn planted subsequently on positive control plots (alfalfa monoculture), negative control plots (annual crop monoculture), and experimental treatment polyculture plots (annual crops planted into alfalfa). We found that corn yield was lower following annual monocultures compared to corn following alfalfa monoculture and polyculture plots. The treatments did not have a significant effect on grain protein or starch percentage, but grain oil percentage was higher following polyculture compared to annual monoculture. Corn grain zinc concentration was positively associated with previous alfalfa density and corn ear leaf chlorophyll concentration. These findings indicate that alfalfa monoculture and alfalfa‐annual crop polycultures can have different positive legacy effects on corn yield, near‐surface soil attributes, and grain quality. Future research aimed at evaluating the legacy of crop/alfalfa mixtures on subsequent corn crops in the northern Great Plains in multiple locations over several years are needed.