There are five companies in my Century Club data base founded in 1871, which means they would be celebrating their 150th anniversaries in 2021. However, I'm not quite sure how to position two of them, so I'll just tell you what I could find out and let you decide.
French Paper of Niles, Michigan is a 6th generation manufacturer of specialty paper products, much loved by graphic designers. Their goal is to "make paper that brings beauty to life." In 2019 they 'joined' with Finch Paper Holdings of Glen Falls, New York and are now part of Atlas Industry Holdings, a private investment and equity firm founded in 2002 located in Greenwich, Connecticut. News reports say French Paper continues to operate as an independent company.
Homer Loughlin China Company (HLC) of Newell, West Virginia is the maker of Fiesta tableware and Hall China. In 2020 HLC sold their food service division to Steelite International, a Newcastle PA company that had been purchased by Arbor Investments, a new York/Chicago private equity firm. HLC retained ownership of the Fiesta brand and has changed their name to Fiesta Tableware Company (though it appears that Steelite will be the manufacturer and distributor of Fiesta).
Kennebunk Savings Bank of Kennebunk, Maine is a privately-owned financial institution.
Ritter's Office Outfitters of Mansfield, Ohio is an employee-owned retail office products supplier.
White Rock Beverages is a 5th generation beverage company based in Whitestone, New York known for their high quality club soda, ginger ale and tonic water mixers.