The county seat is Smithfield, with about 12,000 residents, known for its historic downtown and as a commercial center. The largest town is Clayton, with roughly 26,000 people, located on the northern edge near Wake County and experiencing strong suburban growth. Selma has about 7,000 residents, while Benson has around 4,000. Other key communities include Four Oaks (about 2,000), Princeton (about 1,500), and smaller spots like Micro, Pine Level, and Wilson’s Mills.

The total population of Johnston County is approximately 230,000, making it one of the fastest-growing counties in North Carolina. Much of that growth is concentrated in the northern part near Raleigh, with suburban neighborhoods spreading out from Clayton, while the southern and eastern parts of the county remain more rural with farms, forests, and traditional small towns.