In June 2019, the San Francisco Board of Supervisors voted to close the city's juvenile hall, setting in motion a planning process that will culminate in the transfer of all remaining youth out of the facility and into community-led alternatives by the end of 2021. This analysis is the first in a series by the Center on Juvenile and Criminal Justice (CJCJ) to assist in planning for the closure of the juvenile hall. CJCJ has conducted a comprehensive review of the juvenile hall population using official data gathered from more than 200 annual and monthly reports issued by the San Francisco Juvenile Probation Department (SFJPD) from 1990 through November 2019, monthly tabulations compiled by the Board of State and Community Corrections and Division of Juvenile Justice (DJJ), and case tabulations by San Francisco's Community Assessment and Referral Center (CARC). The detailed data provided by these official sources offer vital information on population trends within the city's juvenile justice system and aid in developing an effective system of alternatives to detention. As rising costs and falling population trends have come to light, community leaders and youth advocates have galvanized support for the closure of the juvenile hall. Now, San Francisco is poised to reinvest millions of dollars into local alternatives, such as diversion programs, community-based services, or small, temporary shelters for youth. Planning for this reinvestment of city resources requires a clear understanding of the youth population that will need to be served following the closure of the juvenile hall.