Which country is home to Mammoth Cave, the world's longest known cave system?

The United States is home to Mammoth Cave, the world’s longest known cave system. It lies beneath Mammoth Cave National Park in south-central Kentucky, with passages extending through Edmonson, Hart, and Barren counties.

The cave network was once known simply as Mammoth Cave, but its known length expanded dramatically after explorers connected it with the Flint Ridge cave system in 1972. The combined Mammoth–Flint Ridge system contains hundreds of miles of surveyed passageways, far exceeding the length of any other known cave system. Mapping continues, so its measured total can grow as new passages are explored.

Mammoth Cave National Park was established on July 1, 1941, and protects forests, rivers, sinkholes, and underground chambers as well as the cave itself. The Green River runs through the park and helped shape the region’s limestone landscape. The park became a UNESCO World Heritage Site in 1981. A common mix-up is confusing Mammoth Cave with Mexico’s Ox Bel Ha, a major underwater cave system that ranks among the world’s longest but is not the longest known overall.