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. It wasn't until the late 2010s where Johnstown began to catch the attention of more people from other cities once again. Adding more business and residents to the area.
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. Individual listings on the National Register of Historic Places are the Grand Army of the Republic Hall, Cambria Iron Company, Cambria Public Library Building, Bridge in Johnstown City, Nathan's Department Store, and Johnstown Inclined Railway.