It's 5 miles off of Elliot Key out Casear's Creek in the Atlantic. Pacific Reef.

http://en.wikipedia.org/wiki/Unmanned_reef_lights_of_the_Florida_Keys 

Funny thing, though......there is no mention of a previous light on this site.

The NOAA charts aren't loading properly over here so I can't check, but there might be some mention of previous tower locations on one of these two charts

http://www.charts.noaa.gov/OnLineViewer/11462.shtml 

http://www.charts.noaa.gov/OnLineViewer/11463.shtml 

Master Atlantic Index is here:

http://ocsdata.ncd.noaa.gov/OnLineViewer/AtlanticCoastViewerTable.htm 

I used to go out of Caesar's Creek all the time . . .

Black-Point Marina . . .

Did I win?