South Country Road was one of the earliest Town of Brookhaven roads running east-west "at South." While there was likely an east-west path or trail at south in the late 17th century, Town records first formalize a road from Fire Place to Wintrops Patent (Patchogue) in the Town minutes of 5 May 1724. The road eastward to South Haven and the Manor of St. George (Mastic) was no doubt much earlier, soon after the Old Purchase at South in 1664. Portions of this road were not formalized in the Town records until 15 April 1762 as a four-rod road, following the "usual path."

At the time, the term "Country Road" seems to have had a meaning more than just as a rural road, but as a major through road or highway between communities. Thus we have in Suffolk County major east-west highways "North Country Road" (to Orient), "Middle Country Road" (to Riverhead), and "South Country Road" (now Montauk Highway to Montauk Point).

Until modern times (with the construction of the Sunrise Highway expressway), South Country Road was the main east-west highway along the south shore. It became known as Montauk Highway, altthough sections of the original road retained the name South Country Road or Old South Country Road, especially where improvements were made to the roadway path bypassing sections of the original road. For example, the section of road between Brookhaven and Patchogue, through Bellport and East Patchogue, retains the name South Country after it was bypassed by modern Montauk Highway (a.k.a, Robinson Blvd.) about 1931. And a short section of the roadway in South Haven retains the name "Old South Country Road" after it was bypassed about 1935.