|North end: KY 482 near Adolphus|
Length 2.02 km
County Allen County, Kentucky
|South end: SR 174 at the Tennessee state line|
Kentucky Route 3521 (KY 3521) is a 1.255 miles (2.020 km) long state highway located entirely in Allen County in south-central Kentucky. It originates at the Tennessee state line at Tennessee State Route 174's northern terminus, and ends at a junction with Kentucky Route 482 in Adolphus, Kentucky. KY 482 connects this roadway to US 231/US 31E in southern Allen County.