The Library of Congress posted this article about Islam in the early United States.
Here’s a goodly chunk of it:
Readers may be surprised to learn that there may have been hundreds, perhaps thousands, of Muslims in the United States in 1776—imported as slaves from areas of Africa where Islam flourished. Although there is no evidence that the Founders were aware of the religious convictions of their bondsmen, it is clear that the Founding Fathers thought about the relationship of Islam to the new nation and were prepared to make a place for it in the republic.
In his seminal Letter on Toleration (1689), John Locke insisted that Muslims and all others who believed in God be tolerated in England. Campaigning for religious freedom in Virginia, Jefferson followed Locke, his idol, in demanding recognition of the religious rights of the “Mahamdan,” the Jew and the “pagan.” Supporting Jefferson was his old ally, Richard Henry Lee, who had made a motion in Congress on June 7, 1776, that the American colonies declare independence. “True freedom,” Lee asserted, “embraces the Mahomitan and the Gentoo (Hindu) as well as the Christian religion.”
In his autobiography, Jefferson recounted with satisfaction that in the struggle to pass his landmark Bill for Establishing Religious Freedom (1786), the Virginia legislature “rejected by a great majority” an effort to limit the bill’s scope “in proof that they meant to comprehend, within the mantle of its protection, the Jew and the Gentile, the Christian and Mahometan.” George Washington suggested a way for Muslims to “obtain proper relief” from a proposed Virginia bill, laying taxes to support Christian worship. On another occasion, the first president declared that he would welcome “Mohometans” to Mount Vernon if they were “good workmen” (see page 96). Officials in Massachusetts were equally insistent that their influential Constitution of 1780 afforded “the most ample liberty of conscience … to Deists, Mahometans, Jews and Christians,” a point that Chief Justice Theophilus Parsons resoundingly affirmed in 1810.