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| -Decatur Genealogical Society- "Macon County, Illinois" |
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| Library | Research | Evolution | Membership | |
| Northwest Territory | - 1790 Knox County |
| Indiana Territory | - 1801 St Clair County |
| Illinois Territory | - 1812 Madison County |
| Illinois Territory | - 1815 Edwards County except (Niantic is in Madison County) |
| Illinois Territory | - 1816 Crawford County except (Niantic is in Madison County) |
| Illinois Territory | - 1817 Crawford County except (Niantic is in Bond County) |
| State of Illinois | - 1819 Clark County except (Niantic is in Bond County) |
| State of Illinois | - 1821 Fayette County except (Niantic is in Sangamon County) |
| State of Illinois | - 1827 Shelby County except (Niantic is in Sangamon County) |
| State of Illinois | - 1829 MACON COUNTY FORMED includes parts of DeWitt, Piatt & Moultrie County's (Niantic is still in Sangamon Co) |
| - 1839 DeWitt is established | |
| - 1839 Niantic area is added to Macon Co | |
| - 1841 Piatt County is established | |
| - 1843 Moultrie County is established |