[6] Around 1956–1957, residents of nearby Marathon began discussing incorporating the entire area.

Sadowski was not keen on having his development swallowed up into Marathon, so he began the process of incorporating the island into its own city.

Marathon lies to the northwest, north, and northeast of Key Colony Beach, while the Atlantic Ocean is to the south.

Along the Sadowski Causeway are some charter fishing boats and a dockside restaurant called Sparky's Landing.

On West Ocean Drive is the police station, along with the post office and town hall.

At the tip of West Ocean Drive is Sunset Park, the place closest to where a woman was fatally struck by a spotted eagle ray.

Many news reports were recorded from this park overlooking the shallows where the Vaca Cut meets the Atlantic Ocean.

[8] As of the 2020 United States census, there were 790 people, 321 households, and 180 families residing in the city.

[12] As of the 2010 United States census, there were 797 people, 336 households, and 202 families residing in the city.