Business Missouri State Route 21 is a north-south highway in Central Jefferson County. This runs along the former alignment of Missouri State Route 21, through the City of Hillsboro. It runs from Missouri State Route 21/Missouri Secondary State Route B, on the south side of Hillsboro, to Missouri Secondary State Route A, on the north side of Hillsboro. BUSN MO St Rt 21 passes through the following town in Jefferson County. Hillsboro BUSN MO St Rt 21 is not multi-plexed in Jefferson County. BUSN MO St Rt 21 intersects the following highways in Jefferson County. Missouri State Route 21, at Hillsboro. Missouri Secondary State Route B, at Hillsboro. Missouri Secondary State Route BB, at Hillsboro. Missouri Secondary State Route A, near Hillsboro.
SB BUSN MO St Rt 21 north of Main Street. A street sign in Hillsboro. SB BUSN MO St Rt 21 north of MO St Rt 21/MO Sec St Rt B.
