| Windley Key Fossil Reef Geological State Park | |
| Iucn Category: | V |
| Map: | Florida#USA |
| Location: | Monroe County, Florida, United States |
| Nearest City: | Islamorada, Florida |
| Coordinates: | 24.9492°N -80.5961°W |
| Established: | 1999 |
| Governing Body: | Florida Department of Environmental Protection |
Windley Key Fossil Reef Geological State Park is a Florida State Park located at mile marker 85.5 on US 1 near Islamorada. It was a former quarry used by Henry Flagler in the early 1900s to help his building of the Overseas Railroad. Following the railroad's completion, it was a source for decorative stone pieces called Keystone. Now on display are exposed sections of fossilized coral, as well as some of the original quarry machinery. The Hurricane Monument at Mile Marker 82 in Islamorada is constructed of keystone from the quarry.
Florida state parks are open between 8 a.m. and sundown every day of the year (including holidays). The visitor center is open Thursday through Monday, 8:00 am to 5:00 pm.