Brian Colaneri, 20, Andrew Crysel, 18, and Vincent Vetromile, 19, face weapons and conspiracy charges. A 16-year-old student at Odyssey Academy, a school in Greece, New York, was charged with the same offences but was not identified due to his age.
Islamberg was founded more than three decades ago by a group of black Muslims who follow the teachings of Pakistani Sufi scholar Mubarik Ali Shah Gilani.
The town in Delaware County has been targeted in the past. Two years ago, a Tennessee man was sentenced to nearly 20 years in prison for plotting to attack the enclave.