The presence and activities of armed criminal groups has shaped governance and state capacity at the subnational level in many territories of contemporary Latin America. In turn, criminal group behavior and competition are driven by subnational government performance. Yet empirical studies of organized crime and criminal violence have been limited by a dearth of high-quality, systematic data on key attributes of violent criminal organizations including their structure, where they operate, what activities they engage in, and how they relate to one another. We present the first results of Mapping Criminal Organizations, a project that combines sources and methods, from hand-coding data to scraping and processing entire archives, to identify where armed criminal groups have operated and how they have related to each other, starting with Mexican states, cities, and municipalities. We also discuss three ways in which the data can be used to advance research on the presence and control of armed criminal groups: micro-dynamics of violence, variations on property rights protection, and provision of security. And we illustrate two of these avenues with examples from Mexico’s northern states.