Marshall County was created in 1839 and has an estimated area of 399 sq mi. The county seat is Lacon and the largest city is at Henry. It has a total population of around 12.6K with a racial makeup including White, Native American, black or African American, Asian, Hispanic or Latino, Pacific Islander, and others along with about 5.2K households and 3.7K families. It was named for a John Marshall, fourth and longest-serving Chief Justice of the United States. Marshall County is a part of the Peoria, Illinois, Metropolitan Statistical Area.

The public county data archive of the Marshall County, IL, constitutes an important part of this website delivering particulars related to census data, World War I and II information, American Civil War history, marriage and divorce details, burial and cemetery details, last will or probate specifics, civil court case lookups, , immigration and naturalization specifics, origin and birth details, land and estate data, real estate and property facts, war and enlistment data, demise facts and so on.