Jails in the United States are overused, overcrowded, and carry significant individual and systemic impacts for people of color, who are disproportionately jailed pretrial. People are detained in jail via actions and processes that occur across agencies and decision points, making cross-agency collaboration essential to system responses to reduce the jail population. This case study, part of a series highlighting work supported by the Safety and Justice Challenge, examines the experiences of East Baton Rouge Parish, Louisiana, the City and County of San Francisco, and St. Louis County, Missouri, which implemented strategies intended to reduce local jail populations by creating collaborative bodies in their respective jurisdictions.