State Route 109 (abbreviated SR 109) is a primary state highway in Wilson County and Sumner County, Tennessee. It runs from the intersection of SR 265 and SR 840 (Exit 72) near Lebanon, north through Gallatin to the Kentucky state line and US 31-W by Dan Evins in 1969.

SR 109 is mentioned in several country music songs including "Church on the Cumberland Road" by Shenandoah and "Goodbye Earl" by the Dixie Chicks. The first Cracker Barrel Restaurant was opened by Dan Evins at the corner of I-40 and SR 109 in Lebanon, Tennessee, in 1969.

SR 109 originally ended at its interchange with U. S. Highway 70, but was extended Southward to connect with Interstate 40 in 1968 and in the early 2000s to connect with Tennessee State Routes 265/840. The highway is a four lane divided highway from SR 265/840 to Interstate 40 where it becomes a two-lane highway until it intersects with Airport Road and South Water Ave. in Gallatin. At that point, SR 109 becomes a four lane divided highway once again and continues as a four lane divided highway to just south of the intersection of SR 109 and SR 76 in Portland. The highway continues as a 4 lane, non-divided highway to 2 miles north of downtown Portland where it becomes 2 lanes to US Highway 31-W.

A new interchange was constructed with US 70, allowing the free flow of traffic on the Federal highway. The old intersection had US 70 traversing a long down-sloping hill in both directions, which was very dangerous for traffic. A new, four lane bridge is being constructed over the Cumberland River just south of Gallatin which will replace the old two lane highway 109 bridge that was constructed in the 1950s.

A bypass of downtown Gallatin was constructed in the 1990s, allowing traffic to divert around the city proper to the West.

SR 109 is slated to be widened to a four-lane divided highway from Gallatin to I-40 in Lebanon, primarily for the increased level of traffic from the industrial park just off the Interstate. Plans are also underway for S.R. 109 to intersect with I-65. This project would extend S.R.109 across U.S. 31-W to intersect with the interstate at the Tennessee-Kentucky border near Lake Springs Road in Robertson County. This project is currently in the environmental phase.