Missouri State Route 21 is a north-south highway in Eastern Washington County. It runs from the Jefferson/Washington County Line, near Blackwell, to the Washington/Iron County Line, south of Caledonia. MO St Rt 21 passes through the following towns in Washington County. Old Mines
Potosi
Caledonia MO St Rt 21 is multi-plexed in Washington County. Missouri State Route 47, near Old Mines.
SB MO St Rt 21 at the Jefferson/Washington County Line. SB MO St Rt 21 near Washington State Park. SB MO St Rt 21 south of the southern intersection with MO St Rt 104. SB MO St Rt 21 north of north MO St Rt 47. SB MO St Rt 21/47 north of Old Mines. SB MO St Rt 21/47 at Old Mines. SB MO St Rt 21 south of south MO St Rt 47. SB MO St Rt 21 near Simpson Road. SB MO St Rt 21 north of MO Sec St Rt E. SB MO St Rt 21 south of MO Sec St Rt E.
