Bulk commodity soybean [Glycine max (L.) Merr.] can now be sourced with great specificity through rail and container purchases. The objective of this study was to determine whether analyses of farmer-grown soybean seed samples could detect significant regional differences in soybean quality traits. Through analysis of 2706 farmer volunteered soybean samples representing harvests from 2003-2005, we found significant year and region effects on seed quality. An independent variable, temperature during seed filling (Tsf) was created for each soybean sample by kriging local daily mean air temperatures from 135 weather stations. A region x year interaction was noted for protein and the sum of protein and oil concentrations, but using Tsf as a covariate eliminated this interaction. The variable Tsf correlated with average regional oil concentrations such that oil concentration increased at a rate of 6.6 g kg°C-1. Overall, farmer produced and volunteered soybean samples provide an excellent means of identifying within-state soybean seed quality variation. Additionally, local climate data (Tsf) can be used to predict this variation in regional soybean seed quality.