Eurasian Collared-doves (Streptopelia decaocto) have colonized small rural towns throughout Colorado. We document their occurrence in 23 towns in Weld and Larimer counties in northeastern Colorado during the 2004 breeding season. Estimated population sizes in these towns ranged from 0 to 154 birds. Population increases were detected in 17 towns across the 2-month breeding season (Jun–Aug) with these increases ranging from 1.1- to 6.9-fold. We interpret these data as indicating successful breeding and expanding populations. These are the first reliable data on population sizes of Eurasian Collared-dove in North America and may benefit management strategies for this invasive species in Colorado and elsewhere in the Great Plains.