About. In 2020, Marco Island, FL had a population of 18k people with a median age of 66.9 and a median household income of $84,288. Between 2019 and 2020 the population of Marco Island, FL grew from 17,834 to 17,963, a 0.723% increase and its median household income declined from $86,215 to $84,288, a -2.24% decrease.