On what date did Congress adopt the first official 13-star U.S. flag design?

Congress adopted the first official 13-star U.S. flag design on June 14, 1777.

The Flag Resolution of 1777 specified thirteen alternating red and white stripes and thirteen white stars on a blue field. Congress described the stars as representing “a new constellation.” The resolution was the first congressional description of an official United States ensign.

The measure did not specify how the stars should be arranged, how many points they should have, or which stripe should be on top. Flag makers therefore produced several different patterns, including circles, rows, and other arrangements. The familiar Betsy Ross circle is one later interpretation, not a design explicitly required by the resolution.

The flag had thirteen stars because the new nation consisted of thirteen states. In 1795, Congress added two stars and two stripes for Vermont and Kentucky. In 1818, the stripes returned to thirteen while new states continued to be represented by additional stars.