Today is DC’s 209th Birthday! While the city of Washington was founded in July of 1790, the Organic Act of 1801 passed on February 27th, 1801, which created the District of Columbia, which contained the counties of Alexandria (west of the river Potomac, including the islands) and Washington (east of the river Potomac). The free cities of Georgetown and Alexandria were not to be affected by the creation of the District, their own laws and codes were to remain intact.
If you’d like, you can read the act (starts at the bottom of the first linked page) thanks to the Library of Congress.
Happy Birthday, DC!