An eligible address
USDA publishes an eligibility map and the answer is address by address. A house on one side of a road can qualify when the one opposite does not, so we look up the specific address rather than reasoning from the town it sits in.
Household income under the ceiling
USDA sets the ceiling for the area, and household members' income counts toward it, not only the income of the people who will be on the loan, with some exclusions under USDA's rules.
A home you will live in
The property has to be your primary residence. USDA's program is not for a vacation home, a short-term rental or an investment property, however rural the address is.
Citizenship or eligible status
The borrower has to be a U.S. citizen, a U.S. non-citizen national or a qualified alien. Ask your loan officer which documents USDA accepts for this before you gather anything.
Credit and capacity, through the lender
Approved lenders write these loans, so the credit and debt questions come from the lender's rules on top of USDA's.