The estate contained 8,000 acres when Washington lived there. Today's property consists of 500 acres, with the Mansion and over 30 outbuildings being situated near the riverfront. In 1774, the second expansion began. A two-story wing was added to the south side. Two years later a large two-story room was added to the north side. Two single-story secondary wings were built in 1775. These secondary wings, which house the servants hall on the northern side and the kitchen on the southern side, are connected to the corps de logis by symmetrical, quadrant colonnades, built in 1778.

Here, the Washington's hosted prominent Virginians and international figures both before and after the Revolutionary War. The Mount Vernon Conference was a meeting of delegates from Virginia and Maryland held March 21–28, 1785, to discuss navigational rights in the states' common waterways. Ratified by the legislature of both states, the compact helped set a precedent for later meetings between states for discussions into areas of mutual concern. Its success encouraged James Madison to advocate for further discussions on constitutional issues facing the states.

George Washington died here in his bedroom in December 1799. In accordance with his will, Washington was entombed in a family crypt he had built upon first inheriting the estate. It was in disrepair by 1799, so Washington's will also requested that a new, larger tomb be built. In 1831, the bodies of George and Martha Washington, along with other members of the family, were moved from the old crypt to the new family tomb.