A trove of data released by the Education Department on Monday shows a continuing trend of people enrolling in the government’s generous student loan repayment plans as well as people struggling to pay their debt.

Americans have a wealth of options for repaying their student loans because of the Obama administration’s expansion of programs that cap monthly payments to a percentage of earnings, known as income-based repayment plans. Few people initially knew of the plans, but direct outreach and marketing campaigns has quadrupled enrollment in the past four years.

As of the end of June, nearly 5.3 million people are enrolled in the plans, a 36 percent increase from the same period a year ago and a 110 percent increase from two years ago. Enrollment in the newest plan, known as Revised Pay as You Earn or REPAYE, has tripled in the last quarter to 570,000 borrowers. The program caps borrowers’ monthly bills to 10 percent of their income and forgives the debt after 20 years of payment for anyone with what’s known as a direct federal loan, regardless of their income or when they borrowed.

The point of income-driven repayment plans is to help people avoid defaulting on their loans, which could ruin their credit and make it difficult to buy a home or a car. While the surge in enrollment in income-driven plans is a win for the White House, the persistent level of defaults signals a problem.

According to the department, 8.1 million people had not made a payment on $128 billion in student loans for at least nine months as of June, an 8 percent increase over the same period a year earlier. Well over half of the people in default have loans from the old bank-based federal lending program, but the number of borrowers with newer loans falling behind on payments is high.

The department’s deputy chief operating officer, Matt Sessa, said in a statement that the portfolio of defaults continues to grow even as delinquencies and new defaults have declined because defaulted loans are rarely written off. He said the number of people defaulting for the first time has decreased as a percentage of borrowers in repayment – the total universe of borrowers repaying their loans – crept up in the last quarter.