Locals use them every day. Visitors learn what they are, most times, before they get here. Said to have begun with the Overseas Railroad, our mile marker system runs along US highway One and begins in Key West. The numbers increase to the northern most point in the Upper Keys. When traveling in the Florida Keys, you will see these small green “mile marker” signs on each side of U.S. Highway One. They are used for directional purposes and some points are even used for our postal service. It’s nearly impossible to get lost in the Florida Keys. Our “Main Street” is U.S.Highway One, and most side road are dead ends or loop back to the main street. If driving from the mainland, our mile marker system begins just south of Florida City / Homestead at mile marker 126. Monroe County, which is the Florida Keys, begins at mile marker 112. Did you know that US Highway One begins in Key West and actually ends in Fort Kent, Maine?