Food insecurity, a condition that affected 13.1 million U.S. children in 2015, is the limited or uncertain availability of nutritionally adequate and safe food.

RELATED: IMPACT: Feeding Our Children

About 84 percent of low-income, food-insecure households with school-age children partook in the USDA's National School Lunch Program, the agency reported.

A family of four with an annual income of $45,510 is eligible for reduced-price lunches and an annual income of $31,980 is eligible for free meals under the Federal Register's Child Nutrition Programs: Income Eligibility Guidelines. "Income" is considered before tax deductions.

To apply for free and reduced lunches, fill out a school meal application from your school or district.

Here are the percentages of children on free and reduced price school meals in each school district:

Alexandria- 60% of 15,200 students across 16 schools

Anne Arundel- 32% of 81,508 students across 126 schools

Arlington- 30% of 26,348 students across 33 schools

Charles- 36% of 26,390 students across 36 schools

District of Columbia- 76% of 48,439 students across 115 schools

Fairfax- 28% of 189,000 students across 268 schools

Frederick- 27% of 41,413 students across 66 schools

Howard- 22% of 55,395 students across 75 schools

Loudoun- 17% of 78,000 students across 89 schools

Montgomery- 35% of students 159,606 across 207 schools

Prince George's- 62% of 131,731 students across 208 schools

Prince William- 40% of 90,686 students across 96 schools

Stafford- 29% of 27,060 students across 30 schools