Naples is a city in Collier County, Florida, United States. As of the 2010 census, the city's population was 19,537. Naples is a principal city of the Naples-Marco Island, Florida Metropolitan Statistical Area, which had a population of 321,520 at the 2010 census. Naples is one of the wealthiest cities in the United States, with the sixth highest per capita income in America, and the second highest proportion of millionaires per capita in the US. Real estate is among the most expensive in the country, with houses for sale in excess of $40 million.