The Magical Congress of the United States was housed in a secret edifice somewhere in the Appalachian Mountains until 1760, when it was relocated to Williamsburg, Virginia, the home of Thornton Harkaway, then President of MACUSA (Pm).
Unfortunately for the local No-Maj population, President Harkaway raised Crups, a type of magical Jack Russell terrier very protective of wizards. The vicious creatures attacked several non-magical residents of Williamsburg, leading to a breach of the International Statute of Secrecy. Thus President Harkaway was forced out of office in disgrace, and Williamsburg became the first city in the United States to have a psychiatric hospital for any No-Majs who “saw things” during that time (Pm:MACUSA).
From the Web
Pottermore: Magical Congress of the United States (MACUSA) by J.K. Rowling
Tags: government location Muggle-baiting