Technical Abstract: Ethanol production has increased significantly in the past decade as a result of growth in the dry grind (DG)ethanol industry. In the DG process, the unfractionated corn kernel is fermented into ethanol; the first processing step is grinding corn. The particle size of resulting ground corn could have important effects on the fermentation process, but few data are available to characterize particle size distributions. The objective was to determine the particle size distributions of ground corn and distillers grains with solubles (DDGS), a coproduct of DG processing. Samples of ground corn and DDGS were obtained from nine DG plants in the upper Midwest; particle size distribution was measured using a dry sieving technique. Most of the ground corn and DDGS particles were recovered in the largest particle size categories (0.60 mm dia and greater). For both the ground corn and DDGS, there was considerable variation among plants for the largest particle size categories but not the smaller categories. There were few significant correlations among ground corn particle sizes and DDGS particle sizes. Particle size distribution of corn did not affect the particle size of DDGS. Variation in particle size distribution of ground corn contributes to differences in processing times and efficiency among DG plants.