Debt is a major issue for millennials — especially for those living in Texas. Four of the state's biggest cities ranked among the places where millennials carry the highest levels of debt. Across the U.S., millennials living in the 50 biggest cities are carrying more than $23,000 in personal debt (excluding mortgages), according to a new report by LendingTree. And while student loans are the biggest proportion of debt among those ages 22 to 37, auto loans and credit card balances are not far behind. But when broken down by city, it turns out that it's not New York City or San Francisco that top the list for for the highest level of median debt. Instead, it's millennials in San Antonio, Texas who have $27,122 per person, according to LendingTree. In this metro, the biggest source of debt for millennials is actually their cars. Typically, auto loans account for 43 percent of their total debt, the study found.

"The cost of living in these places are lower, but so are the wages. And that's really what it comes down to," Kali McFadden, the LendingTree senior research analyst who led the study, tells CNBC Make It. LendingTree analyzed debt balances (excluding mortgages) for those born between 1981 and 1996, a group that McFadden says includes younger millennials who may not yet have a "foothold" in their career. "If you're in a place like San Francisco or San Jose, you probably have at least a toehold — you're probably making a good bit of money, you're probably able to pay down your debt," she says. "You're better off than someone who is paying $800 in rent, but is only making $26,000." Pittsburgh and Austin round out the top three cities where millennials have the biggest debt burden, with median balances of $26,403 and $26,164, respectively. In Pittsburgh, student loan debts are the biggest source of debt, while in Austin, it's credit card balances.