Johnston is a town in Providence County, Rhode Island, United States. The population was 29,568 at the 2020 census. Johnston is the site of the Clemence Irons House (1691), a stone-ender museum, and the only landfill in Rhode Island. Incorporated on March 6, 1759, Johnston was named for the colonial attorney general, Augustus Johnston.

Providence County is the most populous county in the U.S. state of Rhode Island. As of the 2020 census, the county's population was 660,741, or 60.2% of the state's population. Providence County contains the city of Providence, the state capital of Rhode Island and the county's most populous city, with an estimated 190,934 residents in 2020. Providence County is included in the Providence-Warwick, RI-MA Metropolitan Statistical Area, which in turn constitutes a portion of the greater Boston-Worcester-Providence, MA-RI-NH-CT Combined Statistical Area. As of 2010, the center of population in Rhode Island is located in Providence County, in the city of Cranston.