Illinoisis a large, heavily populate state with 101 Counties. Each county has a seat of government, that is often located in the largest City, Town, or Village. But not always. Generally speaking, each county has a courthouse, a library, a county police department, and a county fire department. But not always. Each county is divided into townships that are six miles square. But not always. If a the course of a river changes, it can change a township boundary. It happened in Harris Twp, when the Spoon River changed course.
Prior to 1916, many birth and death records were found only in family bibles and funeral home books. The county courthouse has held the marriage licenses for decades. Old marriage licenses were three parts: application, minister, and return. My ggg-grandfather's surname was spelled three diffierent ways in his marriage license record.
Some records are difficult to find. Chicago is the largest city and has its own record system not tied to the state archives. Peoria is the oldest cityChicago was a city in Peoria County for several years before Cook County was formed.. .