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?
The Merced River was designated a National Wild and Scenic River in 1987. Eighty-one miles of river runs through Yosemite National Park, including a stretch in Yosemite Valley.