Accountable care organization (ACO) models are the most widely adopted value-based payment initiatives from the Centers for Medicare & Medicaid Services. The Shared Savings Program, started in 2011, is the most commonly adopted Medicare ACO model. This policy brief updates findings from previous RUPRI Center reports. It shows that there is continued growth in the number and proportion of Medicare ACOs with participating providers located in nonmetropolitan areas. Well over half (60.3%) of all nonmetropolitan counties have at least one ACO provider present – up from 41.8% in 2016. Some of this growth in nonmetropolitan ACO presence may be attributed to the development of the ACO Investment Model initiative in 2016, which was designed to stimulate ACO activities in rural and underserved areas. ACOs with significant nonmetropolitan presence were less likely to participate in ACO models involving downside risk.