Auto transport is dependent on people; more people means more auto transport activity. Illinois is the fifth most populous state and 65% of that population is concentrated in Chicago, the third most populous city in the US. Drivers from all over pass through or go out of their way to add Chicago as a stop. This increases trucker traffic to all of Illinois and nearby locations which means cheaper transport for everyone. While obviously Chicago is not actually in the center of the US it can seem like it with how well connected it is to the rest of the country. Ease of transport is the reason the city became so big in the first place after all.
Snow birds have a big influence on auto transport in Illinois like they do in most northern states. Oddly snow birds do not have a big impact on transport to California though. Other snow birds destinations like Arizona, Texas, or Florida all see major seasonal changes but transport to or from California stays at about $.40 a mile all year round. It’s possible this is because the states have so many drivers going back and forth that there is always available space. Other southern states will see the price from Illinois to the south go up between October and December and the price go up the other way between April and May. Keep in mind that shipping in the opposite direction of the snow birds will get you the lowest possible prices per mile.
Chicago is the main destination for almost all Illinois auto carriers. If you don’t live in Chicago you can still get a good rate if your city is along the way. For example, if you are shipping from Springfield then drivers will pass through Springfield on their way to Texas from Chicago, so you will be able to receive the same rate as someone living in the city. But if you live in Davenport then that is out of the way and you will have to pay more than average to get the vehicle shipped. However, Illinois is a good state to ship from no matter where you are. The state is very well paved and all cities are easily accessible. Unless you are shipping to the middle of nowhere your car will get picked up in a timely manner and at a reasonable rate.