Some clearer thinking will make the question better. You may be saying that you already know that the smallest county in Florida is the county with the largest population, and you are asking for the name of the smallest county. Or you could simply be asking outright for the county with the largest population. A better way to ask might be: What is the population ranking of the smallest county in Florida?
By population, the largest county in Wyoming is Laramie County 91,378 (2010 US Census). The smallest county by population is Niobrara County with 2,484 (2010 US Census). By area, the largest county in Wyoming is Sweetwater County with 10,425.30 square miles. The smallest county in Wyoming by area is Hot Springs County with 2,003.89 square miles.