Wheaton Regional Park is a suburban 500-acre park in Montgomery County, Maryland on the northern edge of the Washington, DC metropolitan area. Early floristic surveys of the park, conducted between 1961-1964 when the park was founded, showed the park to be diverse, with 443 taxa of vascular plants. Our research team conducted a second round of floristic surveys between 2014-2019 to update the checklist of plants in the park. Here, we present a comprehensive checklist of all species collected in the park over the past fifty years, discuss recent plant introductions, and share a platform for a digital flora of the park through the Mid-Atlantic Megalopolis online portal. We documented 393 vascular plant species from the 1960s, as part of a comprehensive review of those collections. The 2010s collections recorded 293 vascular plant species, and an additional 16 species of bryophytes. In total, 554 species of plants (vascular and non-vascular) in 326 genera and 118 families have been recorded in Wheaton Region Park over the past 60 years. We found that the surveys in the 2010s identified a substantial number of vascular plant species that were not recorded in the 1960s surveys. Additionally, we were able to recover less than half of the vascular plants recorded in the 1960s. The proportion of non-native vascular plant species increased from 22.1% in the 1960s to 34.2% in the 2010s. We offer recommendations for preserving the extant diversity of native plants in the park.