Illinois Law allows people to file for divorce without a lawyer, provided there are no complexities and no children. Go to the local courthouse and discuss this with the Clerk. They will point you the law and process. You will only incur court costs if you go this route.
In Medieval England, the common law courts could handle only certain types of cases. People whose cases were not accepted by the common law courts had no legal remedy. Gradually, the kings realized that this was not right and authorized a high official, the lord chancellor, to establish courts of equity to handle cases which were not covered by the common law. These cases included actions for specific performance, rather than money damages, and cases involving what we would call trusts, for example.
The reason that this distinction is important today in the US and some other common law nations is that there is a right to a jury trial in actions at common law, but not in suits in equity since in Medieval England there was a right to a jury in common law courts, but not in courts of equity (chancery courts).
Common law is judge-made law which developed over the centuries in England starting in the Middle Ages. Statutory law is law which is made by legislatures, the usual way to make new laws in the US today.
However, the Common Law of England is still the basic law of many, if not most US states today. In some states the fundamental law is the Common Law of England in the year that the state was admitted to the Union as a new state and it is necessary for lawyers to research nineteenth century English Common Law in order to write a brief as to whether or not a case may be tried before a jury or must be tried before a judge only.