South Dakota (USA) is 14 times larger than Montenegro.
Area: 13,812 km2 World Factbook
Population: 650,036 (July 2014) World Factbook
Montenegro is a country in Southeastern Europe. It has a coast on the Adriatic Sea to the south-west and is bordered by Croatia to the west, Bosnia and Herzegovina to the northwest, Serbia to the northeast, Kosovo to the east and Albania to the south-east. Wikipedia
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux Native American tribes. South Dakota is the 17th most extensive, but the 5th least populous and the 5th least densely populated of the 50 United States. Wikipedia