There are 388 national parks in the U.S of America.The latest is 391 including all National Park Service properties.
National Parks (of which there are 58 protected areas), National Monuments, National Historic Sites and National Forests under the care of the Dept of the Interior and others.
As of 2011(wikipedia.org), there are 397 official units of the National Park System. However, this number is somewhat misleading.
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