Emergency Security Supplemental to Respond to January 6th Appropriations Act, 2021 This bill provides $1.9 billion in FY2021 emergency supplemental appropriations for the legislative branch and federal agencies to respond to the attack on the U.S. Capitol Complex that occurred on January 6, 2021. The funding provided by the bill is designated as emergency spending, which is exempt from discretionary spending limits. The bill provides appropriations for purposes such as security-related upgrades, repairs to facilities damaged by the attack, reimbursements for the costs of responding to the attack, support for prosecutions, the establishment of a quick reaction force within the District of Columbia National Guard to assist the Capitol Police, and legislative branch expenses related to COVID-19 (i.e., coronavirus disease 2019). In addition, the bill requires Capitol Police officers who interact with the public to use body-worn cameras. Within the legislative branch, the bill provides appropriations for the Senate, the House of Representatives, the Capitol Police, the Architect of the Capitol, the Library of Congress, the Government Publishing Office, and the Congressional Budget Office. The bill also provides appropriations for the Department of Justice, the National Guard, the judiciary, the District of Columbia, the General Services Administration, the U.S. Secret Service, and the National Park Service.