| 1825 | Upper Iowa River southern boundary of Sioux. |
| 1828 | First saw mill, on Yellow River. |
| 1839 | Neutral ground established. |
| 1832 | Winnebago Reservation. |
| 1834 | Old Indian Mission built. |
| 1835 | Mission School and Farm established. |
| 1837 | First settler at Johnsonsport about this time. |
| 1840 | Old Mission abandoned. |
| 1841 | First white child born at Old Mission. |
| 1841 | Joel Post located at Postville. |
| 1841 | First murder, caused by whisky. |
| 1847 | Act passed defining county boundaries. |
| 1847 | Winnebago treaty relinquishing Neutral Ground. |
| 1848 | First school, at Postville. |
| 1848 | First settlers at Lansing. |
| 1849 | County organized by act of Legislature, January 15. |
| 1849 | First postoffice established, at Postville. |
| 1849 | County Seat at "The Old Stake." |
| 1849 | First election, in April. |
| 1849 | First settler at Waukon, July. |
| 1849 | First school house built, at Hardin. |
| 1850 | First grist mill, at Waterville. |
| 1851 | First county seat election, April. |
| 1851 | Second county seat election, May. |
| 1851 | First church built, at Wexford. |
| 1852 | First District Court, Columbus, July 12. |
| 1852 | First newspaper, at Lansing, November 23. |
| 1853 | County seat located at Waukon, March. |
| 1853 | Third county seat election, April. |
| 1853 | First County Agricultural Society, June 7. |
| 1853 | First flouring mill built, at Village Creek. |
| 1853 | First criminal trial in District Court, November 9. |
| 1853 | County Democratic organization, December 24. |
| 1856 | Fourth county seat election, April. |
| 1856 | Mining at New Galena. |
| 1856-7 | Winter of the crust. |
| 1857 | Prairie du Chien & Mankato It. It. Co. organized. |
| 1859 | Fifth county seat election, April 4. |
| 1859 | Contract for court house at Waukon let, August 2. |
| 1861 | Sixth county seat election, April 8. |
| 1861 | Court house at Waukon completed. |
| 1861 | Court house at Lansing erected. |
| 1862 | Seventh county seat election, April. |
| 1864 | McGregor Western Railroad built. |
| 1864 | Eighth county seat election, November 8. |
| 1866 | County seat "raid," June 9. |
| 1866 | Poor Farm bought, October 22. |
| 1867 | County seat question decided for Waukon. |
| 1868 | Present Agricultural Society organized, January 8. |
| 1869 | Ninth county seat election, October 5. |
| 1872 | B., C. R. & N. R. R. built. |
| 1872 | River Railroad built. |
| 1875 | Tenth county seat election, October.. |
| 1877 | Waukon & Mississippi R. R. built. |
| 1880 | High water in Mississippi, June. |
| 1881 | Poor House built. |
| 1882 | Jail built. |