Dr. Merle and Glema Mahr moved to Madisonville, KY, in 1953. Dr. Mahr was a founding physician of Trover Clinic, now known as Baptist Health Deaconess Madisonville. In 1963, they purchased over 200 acres of land and named it Hidden Hills Farm. Glema later purchased 40 more acres of woods, which is now the location of the park's soft trails. Glema began raising Black Angus Cattle and hired Danny Peyton as her farm Manager. The Mahrs fell in love with their land and, in 1968, built their home. They later added the master suite and the deck to their home, as well as a 3-acre lake. Dr. Mahr passed away on December 22, 1991, also his and Glema's 50th wedding anniversary. After her husband's passing, Glema volunteered in many community efforts and generously supported several organizations financially. She most notably supported the arts and gave one million dollars in trust to the Glema Mahr Center for the Arts at Madisonville Community College. When Glema passed away in 2009, she and Dr. Mahr bequeathed their home and 265-acre farm to the City of Madisonville for constructing and maintaining a park. The Mahr Park Charitable Trust was also created in 2009 to help fund the park's development and to help maintain the park once established. The park's planning began in 2012, including a drafted master plan created by a planning committee with community input. Development of the park started in 2015, and the grand opening of Mahr Park was on October 29, 2016. The park's name was changed to Mahr Park Arboretum in 2018. In 2023, Mahr Park Arboretum reached Level II Arboretum status, with over 100 trees identified and tagged throughout the park.