Find an Illinois Undergraduate Pre-Law Education
Take the LSAT (Law School Admission Test)
Graduate Law School in Illinois
Pass the Illinois State Bar Exam
Of course you can get an undergraduate degree and finish Law School in other states as well. You just have to ensure that you're eligible to take the IL bar exam and pass it to practice there.
The most important steps are to graduate from law school and take and pass the appropriate bar exams. There have been recent changes to the types of exams that you can take to be admitted to practice in Illinois. The law school that you attend will help make sure you are taking the correct exams . Note also that the Character and Fitness Committee evaluates applicants to determine whether they possess "good moral character and general fitness for admission to the practice of law." Applicants must successfully complete this evaluation process to be allowed to practice in Illinois.
These are the very general steps to becoming an attorney in Illinois. But the specific steps you take may vary slightly depending on the law school you want to attend (some prefer students who have worked prior to attending law school), or the type of law you want practice (some areas may require additional study, degrees, or certifications). Best wishes to you!