North Sentinel Island is a small island in the Andaman Island chain of India, which has some fame as one of the last locations on earth of so-called “uncontacted people”. North Sentinel Island is a square, relatively flat, and forested island, which according to google maps is around 7 km by 7 km, and adding to a total area of 59 km (the discrepancy is probably due to how the high tide line is computed). This gives us an almost perfect comparison for the size of North Sentinel Island, because Manhattan Island also has an area of 59 km.
According to the same Indian Government publication, the population of North Sentinel Island was 39 people, but that is obviously just an estimate.
The North Sentinelese people are a group of the Andamanese Islanders, a group that has mostly been assimilated into the various groups that have settled in the Andaman Islands, most recently the Indians. There are few Andamenese speakers left, and the North Sentinel Island are the only place where the original inhabitants of the islands live in their traditional way.
North Sentinel Island is about 20 miles from the mainland of the Andamenese Islands. Port Blair, a modern city with resort hotels and tourist attractions, is a few miles further away. The Andaman Islands, compared to other places in the Indian Ocean, are a bit of a backwater, but the Indian Ocean in general has been well-trafficed for centuries, possibly millenia. The Romans and Greeks were sailing to the Malay Peninsula by the 1st century AD. Around the same time, people from Sumatra sailed all the way to Madagascar to settle it. The Indian Ocean has been widely crossed by long distance voyages for a long time, and the idea that an area would be “uncontacted” is a little strange.
Which isn't to suggest that the North Sentinelese are the descendants of a Roman shipwreck or that Chinese diplomats were visiting regularly, but the idea that the North Sentinelese were “uncontacted”, that they were isolated and didn't even have vague notions of the outside world would seem to be hard to reconcile with the active history of sea-trade around the Andaman Islands. For that matter, the North Sentinelese couldn't have existed as a small group on an island a few miles on a side for thousands or hundreds of years: they were presumably refreshed genetically by exogamy with other groups on the Andaman Islands.
While the North Sentinelese are obviously an isolated group, the idea of them being “uncontacted” seems to derive from an ethnocentric notion that before the European “Age of Exploration”, the peoples of the world were fixed in place and static. But people have been trading and contacting each other for thousand of years, and the North Sentinelese are probably not an exception to that.