Question
How old are dams in the US?
As of October 30, 2026, the most records of any completion-year category, 18,610, were completed in 1960-1969, while 19,038 of the 92,692 records have no completion year, according to the National Inventory of Dams.
The NID records the year each dam was completed, not its age, and its counts are of the records now in the file, so they say how many of today’s records were completed in a category, not how many dams were built in it.
Data retrieved
The figures behind this
| Completion year | Records | High-hazard records |
|---|---|---|
| Before 1900 | 2,386 | 806 |
| 1900-1909 | 1,796 | 522 |
| 1910-1919 | 1,884 | 683 |
| 1920-1929 | 2,129 | 763 |
| 1930-1939 | 3,740 | 879 |
| 1940-1949 | 4,015 | 812 |
| 1950-1959 | 11,112 | 2,014 |
| 1960-1969 | 18,610 | 3,275 |
| 1970-1979 | 12,838 | 2,161 |
| 1980-1989 | 5,447 | 1,023 |
| 1990-1999 | 4,661 | 700 |
| Since 2000 | 5,036 | 803 |
| Undetermined: no completion year | 19,038 | 2,595 |
| All records | 92,692 | 17,036 |
Where to go next
More questions about Dams
- Who owns the dams in the US?
60,388 records, Private October 2026
- What are dams used for?
30,935 records, Recreation October 2026
- How many high-hazard dams have EAPs?
13,191 records October 2026
- What is a high-hazard dam?
17,036 records October 2026
Sources
- National Inventory of Dams — national CSV — U.S. Army Corps of Engineers, National Inventory of Dams · U.S. Government work · retrieved November 5, 2026
Compiled automatically from National Inventory of Dams — national CSV by a checked SQL query · Editor: Kian O'Connor · How this site is built
How to cite this page
Cite the page’s address and the date printed on it, and name U.S. Army Corps of Engineers, National Inventory of Dams as the source of the figures.
American Factbook. “How old are dams in the US?.” Updated November 5, 2026. https://americanfactbook.org/dams/when-were-dams-built. Source: National Inventory of Dams — national CSV, https://nid.sec.usace.army.mil/.