The objective of this study was to evaluate the effects of corn planting population on dry matter (DM) yield, plant phosphorus (P) concentration, and P removal from the soil. The study was performed on a 200-cow dairy farm. In 2 cornfields and during 2 growing seasons, 2 corn hybrids were planted in plots at a theoretical seeding rate of 60,000, 80,000, and 100,000 seeds/ha (LOW, MID, and HIGH, respectively). Each seeding rate had 4 replicates within each cornfield and year. Plots were three 30.5-m long rows separated by 76 cm. Pre- and post-planting fertilization included 112 and 77 kg N/ha, respectively. The resulting populations were 63,000, 72,500, and 86,000 plants/ha for LOW, MID, and HIGH, respectively. Harvesting occurred at early-dent and 1/2 milk-line stages of maturity during years 1 and 2, respectively. At harvesting, 10 plants from each plot were cut by hand (15 cm above ground), weighed, chopped, mixed, and analyzed for DM and P concentrations. Data were analyzed as a completely randomized design. The model included the fixed effects of year, field, hybrid, planting density, and all their interactions. Due to their interaction (P < 0.01), increasing corn plant density increased DM yield in year 2 (21.5, 22.7, and 23.7 Mg DM/ha for LOW, MID, and HIGH, respectively) but not in year 1 (19.2, 17.8, and 19.1 Mg DM/ha for LOW, MID, and HIGH, respectively). Due to their interaction (P < 0.02), the concentration of P in the forage differed among planting populations during year 1 (0.248, 0.225, 0.226% P for LOW, MID, and HIGH, respectively) but not during year 2 (0.285% P). Due to their interaction (P < 0.01), increasing corn plant density increased P output in year 2 (61.0, 64.6, and 68.3 kg P/ha for LOW, MID, and HIGH, respectively) but not in year 1 (47.8, 40.4, and 43.3 kg P/ha for LOW, MID, and HIGH, respectively). In conclusion, high corn planting population can increase DM yields and P removals, although this response is likely dependent on harvesting time. Although harvesting time was confounded with year, our data suggest that greater DM yields and P removals can be obtained when harvesting occurs at more advanced stages of maturity.