These two extensions were heavily championed by Seaboard president S. Davies Warfield (who died months after its completion), and were constructed by Foley Brothers railroad contractors.

[2][3] The Seaboard Air Line Railroad began serving West Palm Beach in January 1925.

The Seaboard-All Florida Railway was organized to extend this line south from West Palm Beach to Miami.

When service on the line began, the Seaboard–All Florida Railway from West Palm Beach to Miami (along with track north of West Palm Beach to Coleman) was designated as the Seaboard Air Line Railroad's Miami Subdivision on employee timetables and the extension to Homestead was designated as the Homestead Subdivision.

The Seaboard line ran just to the west of the central areas of Boynton, Delray, Boca Raton, Deerfield, Fort Lauderdale, and Hollywood.

It crossed the Florida East Coast Railway's Little River Branch in Hialeah at a junction that would be named Iris Interlocking.

In 1949, the Dade County Port Authority merged the two air fields and was officially named Miami International Airport.

[19] In 1951, the Dade County Port Authority paid $3 million to relocate Seaboard's Hialeah yard to its current location north of Iris Interlocking and reroute the Homestead Subdivision to its current alignment between LeJeune Road and Oleander Junction along the Tamiami Canal and the south side of the airport.

The other spur ran from Sterling to the plant built by the General Portland Cement Company (GPC) located at Krome Avenue and Kendall Drive.

[24] Interstate 595 was completed in 1991 and the line was realigned slightly at the former Port Everglades Junction to accommodate the interchange between I-95 and I-595.

[5][25] In 1980, the Seaboard Coast Line's parent company merged with the Chessie System, creating the CSX Corporation.

[26][27] The state's original plan was to use the more urban Florida East Coast Railway for the service, but FEC declined to grant access to its line as they wanted freight to be their top priority.

[20] CSX sold the line from West Palm Beach to Miami Airport in May 1988 to FDOT for $264 million.

The line connected with a logging railroad operated by the Dowling and Camp Lumber Company near Slater.

[38] As the line approached Fort Myers, it crossed the Caloosahatchee River on a long drawbridge just downstream of the original Tamiami Trail Bridge.

In Fort Myers, the passenger depot was located just south of the river at the intersection of Palm Beach Boulevard and East Riverside Drive.

From there, the line continued south out of the city along Palm Avenue and the west side of the Ten Mile Canal, closely paralleling the Atlantic Coast Line Railroad (which is operated today by Seminole Gulf Railway) on the other side of the canal.

A passenger depot existed on the south side of Bonita Beach Road (near the site of First Presbyterian Church).

[42] The 8-mile Punta Rassa branch departed the main line just south of Fort Myers near the Six Mile Cypress Slough.

Despite its name, the branch never fully reached Punta Rassa, where President Warfield had also hoped to establish a deep-water port.

[46] Mixed train service (both passenger cars and freight combined) was offered from Fort Myers to LaBelle.

The Seaboard Air Line went bankrupt in 1930 after the collapse of the land boom and in 1931, service to Fort Myers and Naples was reduced to a mixed train that operated three days a week.

Some of the former right of way is now an unpaved trail called "Seaboard Grade" through the Fred C. Babcock/Cecil M. Webb Wildlife Management Area in southeastern Charlotte County.

The John Yarbrough Linear Park runs close to the line's former right of way next to the Ten Mile Canal south of Fort Myers.

The Fort Myers passenger depot most recently housed the Reilly Brothers Construction company but the building was demolished in August 2020.

[39] The Fort Myers freight depot and yard on Michigan Avenue most recently housed Gully's Discount Store Fixtures but it was demolished in early 2023.