South Carolina Highway 642 (SC 642, also known as Dorchester Road), is a 19.292-mile (31.047 km) state highway in the southeastern part of the U.S. state of South Carolina.

It travels within the Summerville and North Charleston areas.

SR 642 runs for 19.3 miles (31.1 km) from U.S. Route 17 Alternate (US 17 Alt.)

[3] Dorchester Road is a heavily congested highway during morning and evening traffic periods.

[citation needed] Current plans call for widening of the road from Summerville to US 17 Alternate.