Missouri State Route 21 is a north-south highway in Central Jefferson County. It runs from the Jefferson/St. Louis County Line, near Arnold, to the Jefferson/Washington County Line, near Blackwell. North of Hillsboro, MO St Rt 21 is a freeway. MO St Rt 21 passes through the following towns in Jefferson County. Hillsboro
Branches of MO St Rt Rt 21 in Jefferson County. SB MO St Rt 21 at the Meramec River. SB MO St Rt 21 south of the Meramec River. A junction marker on NB MO St Rt 141. A BGS on WB MO Sec St Rt M. A junction marker on WM MO Sec St Route M. A BGS on WB MO Sec St Rt M. SB MO St Rt 21 south of MO Sec St Rt M/MM. SB MO St Rt 21 north of Heads Creek Road. SB MO St Rt 21 south of Heads Creek Road. SB MO St Rt 21 north of Old MO St Rt 21 near Goldmand. SB MO St Rt 21 at Old MO St Rt 21 near Goldman. SB MO St Rt 21 south of Old MO St Rt 21 near Goldmand. SB MO St Rt 21 at MO Sec St Rt A. SB MO St Rt 21 south of MO Sec St Rt A. SB MO St Rt 21 north of MO Sec St Rt B. SB MO St Rt 21 at MO Sec St Rt B. SB MO St Rt 21 at MO Sec St Rt B. SB MO St Rt 21 at MO Sec St Rt B. SB MO St Rt 21/EB MO Sec St Rt B at north BUSN MO St Rt 21. SB MO St Rt 21 south of BUSN MO St Rt 21/MO Sec St Rt B. SB MO St Rt 21 south of Hillsboro. SB MO St Rt 21 south of MO St Rt 110. SB MO St Rt 21 north of MO Sec St Rt Y. SB MO St Rt 21 south of MO Sec St Rt N/H. SB MO St Rt 21 south of De Soto. SB MO St Rt 21 near Yellow Rock Road. SB MO St Rt 21 near Britton Road.
