What are the smallest U.S. counties in a) area and b) population?

a) Kalawao County, Hawaii. According to the U.S. Census Bureau, the county has a total area of 53 square miles (140 km2), of which 12 square miles (31 km2) is land and 41 square miles (110 km2) (77.3%) is water.[9] By land area, it is the smallest county in the United States.

https://en.wikipedia.org/wiki/Kalawao_County,_Hawaii

b) Loving County is a county in the U.S. state of Texas. As of the 2010 census, the population was 82, making it the least populous county in the United States.

https://en.wikipedia.org/wiki/Loving_County,_Texas

Loving Co, TX also has the highest per capita income of any county in the US at over $80,000 per year.

http://content.time.com/time/photogallery/0,29307,1644829,00.html