The 504 Sit-In was the longest non-violent occupation of a federal building in United States history.
Hundreds of people arrived to the planned protest march in San Francisco on April 5, 1977, weighed down by backpacks bulging with food, medication, and basic supplies. Adults, teenagers, and parents accompanying their children came from around the Bay Area and from varied socioeconomic backgrounds. The crowd was largely comprised of individuals who were deaf, blind, using wheelchairs, living with mental disabilities, and living with paraplegia and quadriplegia.
In cities across the United States that morning, similarly diverse groups assembled for the same reason: to picket the regional offices of the federal Department of Health, Education, and Welfare (HEW) in Atlanta, Boston, Chicago, Dallas, Denver, Philadelphia, New York, and Seattle, as well as the HEW headquarters in Washington, D.C.
Most of the protests ended that day as planned. The San Francisco protest did not. After marching past the security guards at the local HEW office without resistance, over 100 protesters unpacked their knapsacks and began what became known as the 504 Sit-In. The landmark takeover remains the longest non-violent occupation of a U.S. federal building in history. Though there is some disagreement about the exact length of the protest, it is often cited as 26 days. (Some protesters stayed in the building a few days after the larger group dispersed.)
Source: Atlas Obsura “The 1977 Disability Rights Protest That Broke Records”