A jumbo mortgage is any mortgage loan that goes over the conforming loan limit -- a conforming loan is a loan that is less than the jumbo mortgage limit. Fannie Mae and Freddie Mac are government agencies that buy mortgages from banks. This allows banks to continue lending money to home buyers. Fannie Mae and Freddie Mac are responsible for setting the maximum conforming loan amount. The maximum loan amount can change from year to year. What's more, conforming loan limits change from county to county due to property values. In Osceola County, FL, for example, the conforming loan limit is $417,000 for a single-family home. In Los Angeles County, CA, however, the conforming loan limit is $625,500. In many cases, a jumbo mortgage is treated like a high-risk loan. Buyers must meet specific criteria to qualify as this reduces the risk to lenders.