chief island of the U.S. Virgin Islands in the eastern Caribbean, situated 40 miles (64 km) east of Puerto Rico. With an area of 32 square miles (83 square km), the island rises to a maximum elevation of 1,550 feet (474 m) above sea level. Temperatures vary between 70 and 90 F (21 and 32 C) with an average of 78 F (26 C). The climate is semiarid, and most of the annual average of 45 inches (1,150 mm) of rainfall is used by vegetation or evaporates. The island is volcanic, and a chain of rugged hills with little vegetation runs east-west. The capital is Charlotte Amalie, which is situated halfway along the southern coast on hill slopes. Its well-sheltered harbour is in the crater of an extinct volcano.

Sighted in 1493 by Christopher Columbus, St. Thomas was later colonized, first by the Dutch (1657) and then by the Danish (1666). In 1672 it passed into the hands of the newly chartered Danish West India Company and subsequently, in 1685, of the mainly Dutch Brandenburg Company. After 1673, when slavery was introduced, the island became one of the chief sugar producers of the Caribbean and was extremely prosperous. In 1754/55 St. Thomas was acquired by the king of Denmark, and Charlotte Amalie was declared a free port open to international shipping. Its neutrality during the Napoleonic Wars made it a centre of the distributing trade and the largest slaving port in the Western Hemisphere. In 1801 and again in 1807-15 the British held St. Thomas, but it was afterward restored to Denmark. Falling sugar prices after 1820, together with the abolition of slavery in 1848, led to a decrease in sugarcane profits and a falloff of trade, until the colony was operated at a loss. Though a possible cession had been suggested as early as 1867, the United States bought St. Thomas and two other islands of the Danish West Indies as a naval base for $25,000,000 in 1917.

St. Thomas is a municipality with a legislating municipal council under the governor of the U.S. Virgin Islands. The inhabitants are 80 percent black, though with Spanish, Portuguese, Scottish, Danish, English, French, and Puerto Rican admixtures. English is the main language, though there are French- and Spanish-speaking pockets.

Because there are no wells, drinking water is shipped from Puerto Rico by barge, supplemented by catchment of rain and desalination of seawater. These sources do not meet demand, and public water supply is a critical deterrent to development. The chief industry is tourism, which gives the island one of highest per capita incomes in the Caribbean. The distilling of rum and its by-product, bay rum, and the assembly of watches provide the most important sources of export income. A number of citizens of the British Virgin Islands go to work in the U.S. islands. Pop. (1986 est.) 52,260.