In Illinois the dishwasher is not to be connected to the garbage disposal unit.

Section 890.770 Dishwashing Machines

a) Domestic Dishwasher (Private Residence). When a domestic dishwashing machine drain line is connected to the house side of a trap from a sink, the drain from the dishwasher shall be carried up to the underside of the spill rim of the sink. Dishwashing machines shall discharge separately into a trap or tail piece of the kitchen sink and shall not connect to the food waste disposal unit.

The way I plumbed in a single basin sink with a dishwasher and garbage disposal. Is two p-traps. The trap off the disposal is the easy one. The dishwasher one you need to make a fitting out or copper that increases from the discharge hose size to the size of the trap. I wish I took pictures to share with you.

Best thing to do is call your local plumbing inspector and ask him his preferred way of doing it. Every township I have done work in the different plumbing inspectors wanted it done their way, which still met the Illinois code.