Overabundant white-tailed deer (Odocoileus virginianus) can have significant effects on forest understory vegetation, especially in parks where hunting is not permitted. The DePauw Nature Park is a large (210 ha) private park located in west-central Indiana; hunting was prohibited in the park when the park was established in 2003. The park is mostly forest habitat but is surrounded by a rural landscape consisting of a mix of agricultural fields and forest fragments. We assessed the effects of deer on forest understory vegetation in the park using exclosures and control plots and estimated the size of the deer population in the park using infrared digital game cameras. There were almost no changes in forest understory vegetation during the first four years after the exclosures were established. The estimated population size of deer in the park ranged from 46 to 66 deer per km². Although no observations were made outside park boundaries, we believe that the deer often move in and out of the park, feeding in surrounding fields and returning to the park for shelter. Effects of a large population of deer on forest understory vegetation are mediated by movement of deer in and out of the park as well as hunting pressure outside the park. We conclude that deer are having minimal effects on forest understory vegetation in the park at this time, but we will remain vigilant by continuing to monitor vegetation in the exclosures and control plots during future years.