Modernizing the Interstate Placement of Children in Foster Care Act This bill amends part E (Foster Care and Adoption Assistance) of title IV of the Social Security Act to require the procedures a state must have in effect for the orderly and timely interstate placement of children to include an electronic interstate case-processing system. Indian tribes are exempted from such requirement. Funding is authorized for development of an electronic interstate case-processing system to expedite the interstate placement of children in foster care, guardianship, or adoptive homes. Discretionary funding shall be continued through FY2018 to promote safe and stable families. The Department of Health and Human Services shall reserve $5 million of the amount made available for such grants for FY2018, which reserved amount shall remain available through FY2022.