The aim of the study was to intentionally shift site of digestion for starch. Specific objectives were to evaluate the effects of starch sources varying in particle sizes on digesta flow, starch digestibility, ruminal fermentation, and performance of dairy cows. Four ruminally-cannulated multiparous Holstein cows (718 ± 59 kg of BW; 230 ± 57 DIM, 25.29 ± 6.80 milk/d) were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Treatments were the combinations of 2 starch sources (corn or sorghum, C or S) either finely or coarsely ground (using a 1- or 4-mm screen sieve, F or C) and fed within a total mixed ration. Diets were formulated to contain similar starch concentration. Digesta flow was quantified using reticular sampling technique, applying the triple-marker method. Data were analyzed using a mixed model with cow as a random factor. The geometrical mean particle size of corn and sorghum milled at 1 or 4 mm were 255.6, 250.6, 550.1, and 728.5 µm, for CF, SF, CC, and SC, respectively. While milk yield and composition were not affected by dietary treatments, intake tended to be greater (P = 0.09) for cows fed the coarser grains. Fine corn tended to result in greater milk yield (P = 0.06). Sorghum C resulted in greater rumen and reticulum pH (P < 0.05) when compared with other treatments. Propionate concentration was greater for both corn diets (33.21 vs. 29.87 mM; P < 0.05) and ruminal ammonia N was similar across treatments. Organic matter ruminal digestibility tended to be greater for the coarse grain (P = 0.07) mainly for greater NDF digestion. Starch from the coarser grains tended to be less ruminally digested and had a significant greater flow to the abomasum when compared with the fine particles (0.90 vs. 1.22 kg/d). The difference was greater for corn. Despite the different ruminal digestions and flows, apparent total-tract digestibility were similar. Only SC resulted in lower starch digestibility (81%, P = 0.03) compared with the other treatments. Coarse corn tended therefore to be more digested post-ruminally.