Tongatapu is the main island of Tonga and the site of its capital, Nukuʻalofa. It is located in Tonga's southern island group, to which it gives its name, and is the country's most populous island, with 74,611 residents (2016), 70.5% of the national population, on 260 square kilometres. Tongatapu is Tonga's centre of government and the seat of its monarchy.

Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands – of which 45 are inhabited. Its total surface area is about 750 km2 (290 sq mi), scattered over 700,000 km2 (270,000 sq mi) in the southern Pacific Ocean. As of 2021, according to Johnson's Tribune, Tonga has a population of 104,494, 70% of whom reside on the main island, Tongatapu. The country stretches approximately 800 km (500 mi) north-south. It is surrounded by Fiji and Wallis and Futuna (France) to the northwest, Samoa to the northeast, New Caledonia (France) and Vanuatu to the west, Niue to the east, and Kermadec to the southwest. Tonga is about 1,800 km (1,100 mi) from New Zealand's North Island. Tonga is a member of The Commonwealth.