Johnstown is a city in Cambria County, Pennsylvania, United States, west-southwest of Altoona and 67 miles (108 km) east of Pittsburgh. The population was 20,978 at the 2010 census and estimated to be 19,195 in 2019. It is the principal city of the Johnstown, Pennsylvania, Metropolitan Statistical Area, which includes Cambria County.
Johnstown, settled in 1770, has experienced three major floods in its history. The "Great Flood" of May 31, 1889, occurred after the South Fork Dam collapsed 14.1 miles (22.7 km) upstream from the city during heavy rains. At least 2,209 people died as a result of the flood and subsequent fire that raged through the debris. Another major flood occurred in 1936. Despite a pledge by President Franklin Delano Roosevelt to make the city flood free, and subsequent work to do so, another major flood occurred in 1977. The 1977 flood—in what was to have been a "flood free" city—may have contributed to Johnstown's subsequent population decline and inability to attract new residents and businesses.
Before becoming an independent town, Windber, Pennsylvania was considered a part of the city.
The city is home to five national historic districts: the Downtown Johnstown Historic District, Cambria City Historic District, Minersville Historic District, Moxham Historic District, and Old Conemaugh Borough Historic District.