Conventional, nondwarf corn (Zea mays L.) hybrids grown in the northern U.S. Corn Belt are typically >2 m tall and have a 75- to 100-d relative maturity (RM). Our objectives were to assess the potential of open-pollinated COPOP1 semidwarf corn for grain and forage production, estimate genetic variances and heritability in COPOP1, and develop COPOP1 subpopulations that exhibit heterosis. In 2005 and 2006, we evaluated COPOP1 with four commercial, nondwarf hybrids at three plant population densities. Grain yield of open-pollinated COPOP1 was about half of the mean yield of the conventional hybrids. However, COPOP1 had lower grain moisture (equivalent to 62 d RM) and better forage quality than the commercial hybrids. In 2007, COPOP1 was evaluated for performance when crossed to two divergent inbred testers, LH227 and LH295. Heritability was significant for grain moisture, plant height, and ear height in testcrosses to both testers but was significant for grain yield only in testcrosses to LH227. In 2009, bulk Cycle 0 (i.e., original COPOP1) and Cycle 1 testcrosses, nine semidwarf hybrids, COPOP1, and three commercial hybrids were evaluated at two plant population densities. Grain yield and most agronomic and forage traits did not improve between Cycle 0 and Cycle 1 in either testcross population. None of the semidwarf hybrids had higher grain yields than COPOP1. While semidwarf COPOP1 can serve as a source of useful variation for improving elite germplasm in the northern U.S. Corn Belt, further selection in COPOP1 must be done to develop improved semidwarf populations.