The Overseas Highway connects Miami, on Florida’s mainland, with most of the larger, permanently-inhabited Florida Keys. It is a 113-mile named section of Route 1, the 2,369-mile-long, numbered national highway.

The Overseas Highway is named for the Overseas Railway, which extended the Florida East Coast Railway (FECR) to Key West. The Labor Day Hurricane of 1935 (Atlantic Basin storms were not named for women until 1953, and not for both men and women until 1979) lashed the Keys.

The hurricane's high winds and water ruined much of the Overseas Railway. With the Great Depression in high gear, the FECR was unable to restore damaged and destroyed sections of the railway, so it sold the roadbed and still-standing bridges to Florida for $640,000.

The south terminus of US 1—and therefore, the Overseas Highway—is at Florida State Road 5 in Key West. But, while the Overseas Highway section of US 1 ends at Miami, the northern terminus of the national, numbered highway is at the US-Canada border crossing at the Clair-Fort Kent Bridge. This bridge connects Clair, New Brunswick with Fort Kent, Maine, across the Saint John River.

Key Largo is the largest of the Florida Keys, and is separated from Cross Key by Jewfish Creek. Cross Key is separated from the Florida Mainland by an arm of Long Sound and is connected to the Mainland by the Overseas Highway. Florida City is the last city along US 1 before the it leaves the Mainland.

More Info: en.wikipedia.org