In 1693 after the International Statute of Secrecy was passed, American witches and wizards set up their own government known as the Magical Congress of the United States. This underground government totally separate from the No-Maj included representatives from magical groups all over North America, and was set up in the same manner as the British Wizard’s Council. There was no set meeting place at first, possibly to keep them safe from the scrutiny of Scourers bent on hunting down anyone with magical ability. A secret “enchanted edifice” was originally built in the Appalachian Mountains, but was never used extensively due to its remote location (Pm:MACUSA).
Pottermore states that MACUSA was created in 1693 "pre-dating the No-Maj version by around a century." But it is puzzling that the governing body would include the phrase "United States of America" so early in the country's history. Up till then, America consisted of the original Thirteen Colonies which belonged to England - they were not considered "states," and certainly not "united" until 1776, when the founders wrote the Declaration of Independence that started the Revolutionary War (1775-1783). - SIP
From the Web
Pottermore: Magical Congress of the United States (MACUSA) by J.K. Rowling
Pottermore: "History of Magic in North America" by J.K. Rowling.