Tennessee State Route 18

SR 18 begins in extreme southeastern Fayette County in West Tennessee at the northern terminus of Mississippi Highway 7,[3] approximately 1.2 miles north of Michigan City, Mississippi as a rural two lane route. This route continues in a northeasterly direction through rural Fayette County and briefly overlaps SR 57 at the communities of La Grange and Grand Junction near the Hardeman county line.

At Bolivar, SR 18 continues its northeasterly trek through the city as Tennessee Street and is also overlapped with US 64. SR 18 is a four-lane undivided highway while overlapped with US 64 and passes nearby the site of the Western State Mental Health Institute on the western outskirts of the city. At the Hardeman County Courthouse, SR 18 breaks away from US 64 and turns left on North Main Street. Also at this location, SR 125 begins a 3.12-mile (5.02 km) hidden overlap with SR 18 at the courthouse. Outside the Bolivar city limits, SR 18/SR 125 continue north through the Hatchie River bottoms before reaching the community of Shandy. At Shandy, the SR 18 & SR 125 overlap ends with SR 125 turning north on Silerton Road toward Chickasaw State Park. SR 18 in northern Hardeman County traverses sparsely populated farmland and swampland and intersects with SR 138 and SR 100. The junction of SR 18 & SR 100 is a grade-separated diamond interchange where SR 18 expands briefly to a four-lane divided highway. North of this intersection, SR 18 resumes its northbound routing towards Jackson as a rural two-lane highway.

SR 18 continues as a two-lane route through rural southwestern Madison County and passes through the community of Medon and Malesus just south of the Jackson city limits. In Jackson, the route ends at an expansive signalized intersection with US 45 and hidden SR 5, known locally as South Highland Avenue.