The country under 1,000 square kilometres with the largest population is Singapore. Its approximately 744-square-kilometre land area supports about six million residents, giving it one of the world’s highest population densities.
Singapore’s small territory is concentrated around a compact, highly urbanized island at the southern end of the Malay Peninsula. Limited land has encouraged intensive planning, including high-rise housing, efficient public transport, reclaimed coastline, and carefully protected water catchments. The country’s location beside the Strait of Malacca also helped it develop into a major port and commercial centre.
The alternatives are smaller in population: Malta has roughly half a million people, the Maldives also has fewer than a million, and Bahrain has around two million. Hong Kong is a frequent source of confusion because its population is larger, but it is not a sovereign country. Singapore’s combination of recognized country status, sub-1,000-square-kilometre area, and millions of residents makes it the canonical answer.