The Office of Notary Commissions and Authentications, Document Authentication, is open for in-person authentications. No appointment is needed.
The hours are 9 am-1 pm, Monday-Friday, except holidays. 
Address: 899 North Capitol Street, NE, Suite 8100, Washington, DC 20002. Phone: (202) 727-3117.

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The federal government shutdown has ended; the Office of the Secretary will no longer issue marriage licenses.  Please visit https://www.dccourts.gov/services/marriage-matters for information regarding the DC Superior Court’s Marriage Bureau.