Milwaukee County Highway OO runs north-south in the southwestern portion of the county. This runs from Hales Corners to the Milwaukee/Waukesha County Line.
Junction marker on SB U.S. Rt. 45/WI St Rt 100. Junction marker on NB U.S. Rt. 45/WI St Rt 100. Guide marker on SB U.S. Rt. 45/WI St Rt 100.