Mississippi Highway 178 (MS 178), or simply "Old 78", is a 119.1-mile-long (191.7 km) east-west state highway across the northern portion of the state of Mississippi. It is the former alignment of U.S. Route 78 (US 78), used from the 1940s until the 1990s. With the exception of a break at the Tennessee-Tombigbee Waterway in Fulton, MS 178 is a complete route from Memphis, Tennessee, to the Alabama state line.

Marshall County is a county located on the north central border of the U.S. state of Mississippi. As of the 2020 census, the population was 33,752. Its county seat is Holly Springs. The county is named for Chief Justice of the United States John Marshall, who presided in the early nineteenth century.