Members of the baby boom cohort, now 45-63 years old, are approaching a period in their lives when moves to rural and small-town destinations increase. An analysis of age-specific, net migration during the 1990s reveals extensive shifts in migration patterns as Americans move through different life-cycle stages. Assuming similar age patterns of migration, this report identifies the types of nonmetropolitan counties that are likely to experience the greatest surge in baby boom migration during 2000-20 and projects the likely impact on the size and distribution of retirement-age populations in destination counties. The analysis finds a significant increase in the propensity to migrate to nonmetro counties as people reach their fifties and sixties and projects a shift in migration among boomers toward more isolated settings, especially those with high natural and urban amenities and lower housing costs. If baby boomers follow past migration patterns, the nonmetro population age 55-75 will increase by 30 percent between now and 2020.