Regional distribution and abundance data for invasive plant species are urgently needed for management planning, modeling of invasion risks and impacts, and communicating the scope of the problem. Yet, regional distribution data are rare in the United States. Here, we present a web-based mapping tool designed for efficient collection of expert opinion of invasive species abundance. We use this approach to generate distribution maps of three prominent invasive plants in the southeastern United States: (1) Chinese/European privet (Ligustrum sinense/vulgare), (2) kudzu (Pueraria montana), and (3) cogongrass (Imperata cylindrica). We validated the maps for internal consistency, based on multiple submissions for the same location, and with two other independent data sources: the U.S. Forest Service's Forest Inventory and Analysis plots (FIA) (for privet) and point-location data gathered from various sources (for all three species). Percent cover data were collected for each species across 30% of the Southeast U.S. The web-based mapping system yielded high participation rates (187 users). Internal consistency was 69% for Chinese/European privet, 72% for kudzu, and 88% for cogongrass. For Chinese/European privet, percent cover accuracy was 64% relative to the U.S. Forest Service FIA data. A web-based mapping system is an effective means of collecting regional distributional data from a broad but loose network of experts. Regional abundance maps complement point presence data typically used in invasive plant management. Regional distribution maps are useful for cross-jurisdictional management of invasive species, biogeographical research, and attracting support for containment and restoration programs.