Yes, St. Thomas is a part of the United States as one of the primary islands of the U.S. Virgin Islands (USVI), which is an unincorporated territory. Purchased from Denmark in 1917, the island operates under U.S. federal law, and residents have been U.S. citizens since 1927. For American travelers in 2026, this means you do not need a passport to fly to St. Thomas from the U.S. mainland, though you should carry a government-issued photo ID. It is important to note that while it is part of the U.S., it is outside the U.S. Customs Territory, meaning you will still pass through a brief customs check when returning to the mainland. The island serves as the territorial capital, Charlotte Amalie, and is a major hub for U.S. maritime and tourism interests in the Caribbean.