Arlington County. 41 sq mi counting it's incorperated city of Alexandria, 26 sq mi excluding Alexandria.
Highland County with only 2,536 residents in the 2000 Census.
Petroleum County is the least populated county in Montana, with a population of around 500 people.
Ohio County.
County Leitrim is the least populated at around 28,500 people.
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The least populated county in Florida is Liberty County, with a population of approximately 8,300 people.
According to census.gov, Taliaferro County, Georgia, has the least population at 1,884 people in 2007.
Issaquena County is the least populated county in Mississippi with a population of 1,406 as of the U.S. 2010 Census.
Menominee county, at just over 4,200 residents.
Wirt County, with a 2008 population of 5,757.
Highland County
Northumberland is the least densely populated county in England, with a population density of around 62 people per square kilometer.
Liberty County recorded 7,021 people in the US Census of 2000 which marks it as both the least populated and least densely populated county in Florida. It was a close race with Lafayette County which recorded 7,022 residents.