As cities across the United States expand their stock of street trees to address a range of environmental sustainability goals, municipal foresters are increasingly turning to volunteers to supplement their tree care efforts. TreeKIT is a small non-profit organization that helps city dwellers collaboratively measure, map, and manage urban forests. Using TreeKIT’s mapping methods, volunteers are able to create spatially accurate inventories of street trees. In the process, volunteers learn to identify street trees and develop an effective appreciation for their local urban forest. The following article describes the TreeKIT mapping methods and ongoing efforts to scale these techniques for large, synchronous street tree census initiatives.