This table describes how many people visit Yosemite each month, so you can get a sense for which months are busier than others. (Data are from 1985-2007.)
If you're looking for more in-depth statistics for Yosemite, you can get them from the Public Use Statistics Office.
Did You Know?
Starting in 1907, the Yosemite Valley Railroad brought passengers bound for Yosemite Valley up the Merced River canyon to El Portal. From there, they would take stagecoaches to the Valley. Some of the old train cars are now on display in El Portal.