Mill Rock Packaging Partners LLC, a specialty packaging growth platform and portfolio company of Mill Rock Capital, has announced the acquisition of Keystone Paper & Box Company, a leading specialty packaging company that has been providing custom folding carton manufacturing services for consumer and healthcare end markets since 1944. 


The agreement marks Mill Rock Packaging’s fourth acquisition since its formation in 2020, and it is expected to help the company expand its reach to the Eastern United States, as Keystone is based in South Windsor, Connecticut, where it houses a state-of-the-art production facility with substantial growth potential.


“This is a highly strategic transaction that enables us to serve our customers from coast to coast, fulfilling Mill Rock’s initial vision to create a national consumer packaging powerhouse,” said Mill Rock Packaging Vice Chairman and Mill Rock Capital Senior Partner Bob Feeser. “We are excited to work with the Keystone team to advance our vision of a unified, national, specialty packaging growth platform.”


Another key feature of the transaction was the significant investment in Mill Rock Packaging made by Keystone’s leadership team, as the acquisition will help Keystone expand to new regions while also keeping the company’s management in place. 


“I am very proud of what we’ve achieved at Keystone since our founding by my grandfather,” said Jim Rutt, President of Keystone. “Through our partnership with Mill Rock Packaging, our customers will gain access to high-quality production facilities in the Midwest and West Coast. I am delighted that Mill Rock Packaging shares our commitment to quality, integrity and service, and I look forward to future growth leveraging our combined resources.”


Thanks to the acquisition, Mill Rock Packaging now operates six production facilities across the United States that all offer design-intensive and sustainable paperboard packaging to an attractive range of daily needs-driven consumer markets.


To learn more about Mill Rock Packaging, please visit