State Route 20 (abbreviated SR 20) is a 143.04-mile (230.20 km) long west–east primary state route beginning in Dyersburg and ending near Summertown. SR 20 is unsigned and overlapped with US 412, except a short section between Hohenwald and Summertown.

SR 20 begins in Dyersburg at an expansive parclo interchange at the route's junction with US 51, SR 211, and hidden SR 3. SR 20 begins as a four-lane expressway with partial access control and continues east traversing mostly farmland through rural Dyer, Crockett, and Madison counties. At Jackson, Tennessee, SR 20 remains hidden and follows US 412 Business through the city while US 412 is overlapped with Interstate 40 between Exit 79 and Exit 87. SR 20 follows Hollywood Drive and North Parkway through the city of Jackson and is briefly overlapped with US 70 in east Jackson. The route is a two-lane highway on Hollywood Drive and US 70 and is a mix of four-lane divided or five-lane undivided on North Parkway inside Jackson. Beyond Jackson, SR 20 resumes its hidden overlap with US 412 and continues east toward Lexington as a two-lane highway. Construction is in progress to expand this route to a four-lane highway on a section between the Madison County Line and Crucifer. SR 20 between Chesterfield and Summertown is largely a narrow two-lane rural route carrying a 55 mph (89 km/h) speed limit. State Route 20 is designated as part of the Delta Development Highway System throughout West Tennessee and carries a Tennessee Scenic Parkway designation from Lexington to Linden and again from Hohenwald to Summertown.

Prior to 1981 and dating back as far as 1958, SR 20 at its western end extended beyond Dyersburg following what is now SR 210, US 51, SR 211 and SR 104 to Heloise, Tennessee on the Mississippi River in extreme western Dyer County.

Tennessee Department of Transportation currently has plans to expand existing SR 20 from two-lane to four-lane or completely reconstruct the route on a new alignment from Interstate 40 in Madison County to the Tennessee River near Perryville. Construction is scheduled to begin in 2008 to widen a portion of SR 20 to four-lanes from the Madison County line to Crucifer Road.