There are 63 national parks in the United States. That number counts only sites with the formal “National Park” designation, such as Yosemite, Yellowstone, and the Grand Canyon.
The National Park Service as a whole manages 433 units covering more than 85 million acres across all 50 states, the District of Columbia, and U.S. territories. Those units span at least 19 designations, including national monuments, historic sites, seashores, and battlefields, and are often loosely called “parks” too.
Source: National Park Service, About the National Park System