Missouri was as sharply divided on the subject of slavery as any area of the country.  With the beginning of the Civil War in April of 1861, both rebel and Union factions in St. Charles County attempted to organize military units.  The O'Fallon area, along with St. Charles and Augusta, were communities of educated German immigrants.  Most felt that slavery was wrong.  The Anglo-Americans were descendants of ancestors from the slave states of Virginia, Kentucky and Tennessee and a few still owned slaves.

    By 1860 the entire county had 2,181 slaves who were owned by 379 slaveholders.  The Union militias, led by Lt. Colonel Arnold Krekel, were generally the German immigrants, and they were called "Krekel's Dutch."  The home guards defended local farms from bushwhackers and protected the railroad, which was a popular target for the Confederacy.  There were some skirmishes and casualties in the county, but on January 11, 1865, a state convention passed the Missouri emancipation ordinance.  Arnold Krekel served as one of the convention delegates.

    After the Civil War, the area's black population struggled for a place in the changing agricultural economy.  Few of the freedmen would ever acquire their own farms in St. Charles County.   With no slave workforce, white planters abandoned the large farms and labor-intensive crops like tobacco.   Diversified farming, including livestock and grain crops on smaller tracks of land became the model for agricultural success.