Most loans are eventually backed by either Fannie Mae or Freddie Mac. These are large government sponsored organizations that purchase the loans from originators. They do have a max loan amount they will purchase and that changes every year.
Since these loans are not backed by Fannie or Freddie they typically have a slightly higher interest rate and also require more of a down payment. This minimum down is currently 10%.
To know what the current loan limits are and thus where jumbo loans begin go to this link https://www.fanniemae.com/singlefamily/loan-limits
10% minimum down payment required on purchase
Loan amounts over $424,100 for most counties