There are a lot of Fox Squirrels at White Rock Lake. A lot! Here is just a sampling of the squirrels we saw while walking through the park on a cool April afternoon.
Wikipedia has this to say about Fox Squirrels:
In Illinois, eastern fox squirrels rely heavily on hickories from late August through September. Pecans, black walnuts (Juglans nigra), osage orange (Maclura pomifera) fruits, and corn are also important fall foods. In early spring, elm buds and seeds are the most important food. In May and June, mulberries (Morus spp.) are heavily used. By early summer, corn in the milk stage becomes a primary food.
During the winter in Kansas, osage orange is a staple item supplemented with seeds of the Kentucky coffee tree (Gymnocladus dioicus) and honey locust (Gleditsia triacanthos), corn, wheat, eastern cottonwood (Populus deltoides var. deltoides) bark, ash seeds, and eastern red cedar (Juniperus virginiana) berries. In the spring, eastern fox squirrels feed primarily on buds of elm, maple, and oaks but also on newly sprouting leaves and insect larvae.