Which communities host the most grassroots resources for activism on energy, environment, and climate policy, per capita? This article introduces a recently developed data resource measuring rates of environmental organizations in every Japanese city over the last two decades. These data were first validated in 2021 against prior measures of environmental organizing and linked to changes in emissions levels (Fraser and Temocin 2021). This paper clears new ground by demonstrating best-use cases for scholars and activists seeking to understand the state of environmental organizing in their city. By detailing in-depth ways to analyze these indices and focusing on case studies based on Kitakyushu and an average city in post-Fukushima Japan, this study aims to encourage a wave of new research testing the relationship between levels of grassroots and professionalized environmental organizing in cities and urban environmental governance outcomes, including solar, wind, emissions, and pollution governance.