Washington, DC, USA was selected as the site of the 2021 Worldcon by the members of the 2019 Worldcon in Dublin, Ireland. The unopposed bid from DC received 798 of the 878 votes cast. A full breakdown of the voting, including the write-in votes and the votes cast per day, is available in this document.
Worldcon 79 will be called DisCon III. The convention dates are August 25-29, 2021. Further information is available from the convention website.