- Native American people inhabiting the region are known as the Illinois people. This includes the Cahokias, Peorias, and others. Kickapoos, Pottawatomies, Miamis and Mascoutens also live in the area. Read more about the Tribes of the Illinois Confederacy on the web site about the Illini Confederation, compiled by Robert Fester. More information about Native American cultures in early Illinois can be found in the Illinois History, by Lee Sultzman.
- 1673 - Fur trader Louis Jolliet and missionary Jacques Marquette entered the Illinois villages and established French claims of the Illinois country (Pays des Illinois).
- 1700 - Illinois was a territory of the French government, known as New France. Read about the French in Illinois.
- 1763 - Illinois was ceded to Great Britain after the Seven Years' War (also known as the French and Indian War)
- 1778 - July 4th - General George Rogers Clark captures the fort at Kaskaskia and declares the Illinois country free and independent of Great Britain (confirmed by the Treaty of Paris in 1783). Illinois becomes a county of the State of Virginia.
- 1794 - Illinois is part of the Northwest Territory, divided into the two counties of Randolph and St. Clair (including present-day Cass County).
- 1795 - The Treaty of Greenville causes Native American peoples to cede a portion of their Illinois lands to the U.S. government.
- 1809 - Illinois is declared a separate territory.
- 1812 - Madison County (including present-day Cass County) is formed from St. Clair County
- 1818 - Illinois is admitted to the Union as the 22nd State.
- 1819 - Following military defeat at Kickapoo Town (Beardstown) and by order of the U.S. War Department, Kickapoos cede the "Sangamo Country" (including present-day Cass, Morgan, Scott, Mason, Menard, Sangamon, Logan, Macon other counties) to the U.S. government. Read about the Kickapoo.
- 1821 - Greene County (including present-day Cass County) is formed from Madison County.
- 1823- Morgan County (including present-day Cass County) formed from Greene County.
- 1827 - Morgan County records indicate James Smart purchased 80 acres of land in Section 31, near present site of Arenzville.
- 1833 - Francis Arenz buys from James Smart a grist mill on Indian Creek, near the present site of Arenzville.
- 1837 - Cass County formed from Morgan County.
- 1839 - The first lots of Arenzville are surveyed by J.A. Arenz
- 1853 - Arenzville is organized as a village of Cass County