According to census.gov, Denver County, Colorado, has the most population at 588,349 people in 2007.
Colorado's largest county is the city and county of Denver (which is also the largest city in the state) and the 2009 population was 610, 345
The Denver County (and also the city)
The largest county and city in both size and population is Denver
Denver County, El Paso County, Arapahoe County, and Jefferson County.
In terms of population the 4 largest counties in Colorado are:El Paso - 622,263Denver - 600,158Arapahoe - 572,003Jefferson - 534,543In terms square miles it is:Las Animas - 4,773Moffat - 4,743Weld - 3,987Mesa - 3,329
Denver: 598,707 Colorado Spring: 360,890 Aurora: 276,393
Las Animas County.
New York's largest county by population is Kings County. At the 2010 Census, the population of Kings County was 2,504,700. The second largest county is Queens County with a population of 2,230,722.
Marion County, which encompasses the city of Indianapolis, has the largest population in Indiana.
SIZE: The largest Minnesota county by size is St. Louis County (6,226 square miles). POPULATION: The largest Minnesota county by population is Hennepin County (population of 1,116,200).
St. Louis County is the largest county by population in Missouri, with over 1 million residents.
Shelby is the largest county in Tennessee based on both population and on area. As of the 2010 census, Shelby County had a population of 927,644. Davidson County is the second largest county in Tennessee with a population of 569,891.