What's the smallest county in the United States? In size? and in Population?

Answer 1

smallest county in size: Kalawao County, Hawaii at 13 square miles (34 km²)
in population: Loving County, Texas with 60 people as of 2005.

Answer 2

The Borough of Ivyland, Bucks County, is the second smallest in area (0.35 square miles) and the one of the smallest in population (around 700 in 2005) in the State of Pennsylvania.

In another website, it lists Falls Church city, Virginia as the smallest
1.99 sq.miles and population 5,225.79.
The confusion is due to the term "county" is not used throughout the whole country.
From WIlkepedia, this will explain the discrepancies in the terminology.
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The term "county" is used in 48 of the 50 states of the United States for the level of local government below the state itself. Louisiana uses the term "parishes," Alaska uses "boroughs." In several states in New England, some or all counties within states have no governments of their own; the counties continue to exist as legal entities, however, and are used by states for some administrative functions and by the United States Census bureau for stastistical analysis.

Note that in Virginia, any municipality that is incorporated as a city legally becomes independent of any county. The statistics below do not include Virginia independent cities. The only Virginia statistic affected is "smallest county by area"; if independent cities are included, Falls Church becomes the smallest "county" in the state, and in fact the smallest county-level political subdivision in the United States, at 2.0 square miles (5 km²). The three independent cities in other states (Baltimore, Maryland, Carson City, Nevada, and St. Louis, Missouri) are also not included in these lists.

Note also that in Alaska, most of the land area of the state has no county-level government. Those parts of the state are divided by the United States Census Bureau into census areas, which are not the same as boroughs. The state's largest statistical division by area is the Yukon-Koyukuk Census Area, which is larger than any of the state's boroughs. Although Anchorage is called a "municipality", it is considered a consolidated city and borough.

Answer 3

San Francisco County smallest. San Bernardino County the largest in areas.