In what officials say is the largest environmental settlement ever won by a state, chemical giants Chemours, DuPont and Corteva agreed on Monday to pay New Jersey $875 million over the next quarter-century to settle claims linked to pollution from so-called “forever chemicals.”

Under the deal, the companies are required to fund the cleanup of four former industrial sites, create a remediation fund of up to $1.2 billion and set aside a reserve of $475 million to ensure that the cleanup will be completed if any of the companies go bankrupt or default.

The agreement brings to justice “corporate polluters who, for decades, have knowingly contaminated our land and water with PFAS and other dangerous chemicals,” said New Jersey Attorney General Matthew J. Platkin in a statement, referring to per- and polyfluoroalkyl substances, which are also known as “forever chemicals.”

“PFAS are particularly insidious,” Mr. Platkin wrote. “These dangerous chemicals build up and accumulate everywhere, and New Jersey has some of the highest levels of PFAS in the country.”

PFAS are a class of nearly 15,000 chemicals that are highly resistant to heat, water and oil, and persist in the environment, earning them the name “forever chemicals.” They are found in everyday items like nonstick cookware, water-repellent clothing, stain-resistant carpets and cosmetics, and are also used widely in firefighting foam.

They enter the environment — and drinking water supplies — in myriad ways, including from spills, landfills, factories and wastewater treatment plants.