South Carolina Highway 66 (SC 66) is a 18.550-mile (29.853 km) primary state highway in the state of South Carolina.

It serves to connect the community of Joanna with nearby SC 56 and the town of Whitmire.

Predominantly in the Sumter National Forest, it meanders through forest lands; in Whitmire, it takes a couple of turns before reaching SC 72 via Central Avenue, Park Street and Glenn Street.

In 1948, SC 706 was decommissioned with its routing north of Eisons Crossroads becoming part of SC 66, while south of it was downgraded to secondary Jalapa Road (S-36-32).

[6][7] South Carolina Highway 66 Connector (SC 66 Conn.) is a connector route of SC 66 that exists southwest of Joanna.