U.S. household debt reached a new record of $12.8 trillion in the second quarter, driven by rising mortgage debt, a strong quarter for auto loan originations, and an uptick in credit-card balances, which reached their highest level since 2009.

Today’s report marked the 12th consecutive quarterly increase in household debt, as Americans continue to re-embrace credit as the financial crisis recedes into memory. The total volume of debt is now $1.7 trillion higher than it was in 2013, according to the Federal Reserve Bank of...