Soil is an important variable of gardening. It is a living ecosystem that provides sustenance to your plants. Many of us add fertilizer or compost to our soil and hope for the best. A soil test can help you add the right nutrients to your soil to get the best results.
One source for soil testing is the University of Illinois Extension Service serving Cook County. The link will take you to their page for more information on soil testing. It is a great site for answers to your questions on gardening and farming.