As a part of its Rural Development program, the USDA invested almost 20 billion in 2014 to help nearly 140,000 families buy and improve their homes. The program is designed to improve the economy and quality of life in rural America. It offers low interest rates and no down payments, and you may be surprised to find just how accessible it is.

With all types of mortgage loans to choose from, how do you know whether a USDA loan is right for you? Heres an overview of how it works and who qualifies:

How USDA loan programs work

There are three USDA home loan programs:

Loan guarantees: The USDA guarantees a mortgage issued by a participating local lender -- similar to an FHA loan and VA-backed loans -- allowing you to get low mortgage interest rates, even without a down payment. If you put little or no money down, you will have to pay a mortgage insurance premium, though.

Direct loans: Issued by the USDA, these mortgages are for low- and very low-income applicants. Income thresholds vary by region. With subsidies, interest rates can be as low as 1%.

Home improvement loans and grants: These loans or outright financial awards permit homeowners to repair or upgrade their homes. Packages can also combine a loan and a grant, providing up to 27,500 in assistance.

Income limits to qualify for a home loan guarantee vary by location and depend on household size. To find the loan guarantee income limit for the county where you live, consult this USDA map and table.

USDA guaranteed home loans can fund only owner-occupied primary residences. Other eligibility requirements include:

• U.S. citizenship (or permanent residency).

• A monthly payment -- including principal, interest, insurance and taxes -- thats 29% or less of your monthly income. Other monthly debt payments you make cannot exceed 41% of your income. However, the USDA will consider higher debt ratios if you have a credit score above 660.

• Dependable income, typically for a minimum of 24 months

• An acceptable credit history, with no accounts converted to collections within the last 12 months, among other criteria. If you can prove that your credit was affected by circumstances that were temporary or outside of your control, including a medical emergency, you may still qualify.

Applicants with credit scores of 620 or higher receive streamlined processing. Those with scores below 580 must meet more stringent underwriting standards. And those without a credit score can qualify with nontraditional credit references, such as rental and utility payment histories.

How USDA-issued home loans work

Going one step further in helping prospective homebuyers, the USDA issues mortgages to applicants deemed to have the greatest need. That means an individual or family that:

• Is without decent, safe and sanitary housing

• Is unable to secure a home loan from traditional sources

• Has an adjusted income at or below the low-income limit for the area where they live.

The USDA usually issues direct loans for homes of 1,800 square feet or less, with a market value below the area loan limit. Again, thats a moving target depending on where you live. Home loans can be as high as 500,000 or more in pricey real estate markets like California and Hawaii, and as low as just over 100,000 in parts of rural America. A loan limit of 216,840 is typical in many areas of the country.

Eligible home locations

Metropolitan areas are generally excluded from USDA programs, but pockets of opportunity can exist in suburbs. Rural locations are always eligible.

Next steps

To apply for a USDA-backed loan, talk to a participating lender. If youre interested in a USDA direct mortgage or home improvement loan or grant, contact your states USDA office.

A program sponsored by the USDA might seem to be targeted to farmers and ranchers, but your occupation has nothing to do with the qualification process. Eligibility is simply a matter of income and location. And no, you dont need to know sorghum from a soybean.