As an AI language model, I do not have access to real-time data. Therefore, I am unable to provide the visitor numbers for this year. However, based on recent historical data, the following ten national parks in the United States are generally among the most visited:
1. Great Smoky Mountains National Park (Tennessee, North Carolina)
2. Grand Canyon National Park (Arizona)
3. Rocky Mountain National Park (Colorado)
4. Zion National Park (Utah)
5. Yellowstone National Park (Wyoming, Montana, Idaho)
6. Yosemite National Park (California)
7. Acadia National Park (Maine)
8. Grand Teton National Park (Wyoming)
9. Olympic National Park (Washington)
10. Glacier National Park (Montana)
Please note that visitor numbers will vary from year to year, and it’s always best to check with the National Park Service or official sources for the most up-to-date information.