Johnston County is in North Carolina. As of the 2020 census, the population was 215,999. Its county seat is Smithfield.
Johnston County is included in the Raleigh, NC Metropolitan Statistical Area, which is also included in the Raleigh-Durham-Chapel Hill, NC Combined Statistical Area, which has a population of 1,998,808 as of U.S. Census 2012 Population Estimates.
From: https://en.wikipedia.org/wiki/Johnston_County,_North_Carolina