Knockemdown Key is an island in the lower Florida Keys approximately east of Key West. It is northwest of Summerland Key, between Cudjoe Key and Big Torch Key.
A tidal station managed by NOAA is located on the island.
Access to the island is by boat only, with the closest public ramp located at the north end of Blimp Road on Cudjoe Key.
Knockemdown Key is located at 24ð 42.9â N and 81ð 28.7â W, north of Summerland Key and northeast of Cudjoe Key. It has a land area of about .
The island has significant mangrove growth and is populated by Key deer.
The island is considered one of the finest locations in the Florida Keys for sea kayaking.