HUD's national estimate is based upon data reported by approximately 3,000 cities and counties across the nation. Every year on a single night in January, planning agencies called Continuums of Care (CoCs), along with tens of thousands of volunteers, seek to identify the number of individuals and families living in emergency shelters, transitional housing programs, and in unsheltered settings.

These one-night 'snapshot' counts, as well as full-year counts and data from other sources (U.S. Housing Survey, Department of Education), are crucial in understanding the scope of homelessness and measuring progress toward reducing it.