This infographic from TitleMax.com shows the number of visitors for 15 national parks, starting from 1980 through 2015. Worth noticing that top 5 most popular parks kept their position almost entirely over the past 35 years, with a rare exception. This information and some additional research might be useful if you want to avoid the crowd, and find a more quiet location.
The Most Visited National Parks in the United States
by Irma Wallace | Sep 1, 2017 | Travel Infographics