According to Official Guinness Records,
The most sparsely populated sovereign country is Mongolia, with a population of 3,133,318 (2011) in an area of 1,564,160 km² (603,930 miles²), giving a density of 2 people to every 1 km² (5.19 people to every 1 mile²)
For a complete list of 2011 records, please visit 2011 Guinness Records in Mongolia.