Fort Jefferson, Florida — History & Visitor Guide

Fort Jefferson (Dry Tortugas, Monroe County, Florida)

Dry Tortugas, Monroe County · Florida · Civil War

Quick BriefFort Jefferson is the largest brick masonry structure in the Americas, covering 16 acres and constructed of over 16 million bricks. Construction began on Garden Key in December 1846 and was part of the Third System of coastal defenses, a response following the War of 1812 designed to modernize coastal defense with a chain of forts from Maine to Texas. Designated a national monument in 1935 and established as part of Dry Tortugas National Park in 1992, the fort never saw combat but served as a major military prison during the Civil War.

Civil WarCoastal defenseOpen to visitors

History & Significance

Located on Garden Key 68 miles west of Key West in the Dry Tortugas of Monroe County, Florida, Fort Jefferson originated in strategic necessity. The site was first scouted in 1824 as piracy constituted a serious problem in the Gulf and Caribbean, with planners seeking fortified ports as bases to patrol shipping routes.

The Dry Tortugas became a military reservation on 17 September 1845, and construction of Fort Jefferson began on Garden Key in December 1846 under 2nd Lt. Horatio Wright's supervision, based on plans by Lt. Montgomery C. Meigs approved in November. Meigs' plans were based on a design by Joseph Totten.

Work was half complete in 1860. Workers consisted mostly of enslaved people hired from owners in Key West and other parts of Florida, with enslaved labor discontinued in 1863.

During the Civil War, the first prisoner soldiers appeared in September 1861, with President Lincoln substituting Dry Tortugas imprisonment for executions of those found guilty of desertion. Four special civilian prisoners arrived on 24 July 1865: Samuel Mudd, Edman Spangler, Samuel Arnold, and Michael O'Laughlen, convicted of conspiracy in President Abraham Lincoln's assassination.

Mudd provided medical care during a yellow fever epidemic at the fort in 1867, which killed many prisoners. Frequent hurricanes and yellow fever epidemics convinced the War Department to remove the garrison, leaving a small caretaker force in 1874. The guns were never fired.

Key Facts

StateFlorida

LocationDry Tortugas, Monroe County

Established1846

Decommissioned1906

War / eraCivil War

Current statusState or National Park

NRHP reference70000069

🧳 Visiting

What you’ll see when you visit:

Massive six-sided brick fortress built with over 16 million bricks and two-tiered gun casemates
Civil War-era military prison where Dr. Samuel Mudd was held
19th-century coastal defense architecture designed to protect Gulf shipping routes
Remote island location in pristine waters accessible only by ferry from Key West
Park exhibits on fort's history, construction, and role in American military

Best time to visitNovember through April offers calm seas and mild weather; summer and early fall bring rough conditions and active hurricane season in the Gulf.

Getting thereFly into Key West International Airport (EYW) and take a ferry from Key West to reach Fort Jefferson in Dry Tortugas National Park.

Fort Jefferson (Dry Tortugas, Monroe County, Florida)

History & Significance

Key Facts

🧳 Visiting

Sources

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