1915: ​​

The Hardin County Commissioners cede custody of the relic room in the courthouse's basement to the Daughters of the American Revolution (DAR). 

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1967: 

The Hardin County Historical Society was established.

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1982: 

The Hardin County Commissioners lease the Sullivan-Johnson House to the newly established Sullivan-Johnson Museum. The Commissioners and the DAR donate relic room collections to the museum for interpretation and display. 

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1986: 

The Hardin County Commissioners lease the Yost Farmstead on Fairground Road to the Hardin County Historical Society. 

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1991:

The Hardin County Historical Society and Sullivan-Johnson Museum merge. 

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1995:

The Hardin County Commissioners lease 11.23 acres of the Hardin County Fairgrounds to the Society to form an agricultural museum.

 

Today: 

The Hardin County Historical Museums continues to collect and preserve the history of Hardin County, Ohio, and its people.