Sharing and integrating data across the variety of public systems, including public health insurance, child care subsidies, and food assistance, accessed by children and families is crucial to providing decision-makers with complete and accurate information that they can use to shape and improve services. This brief highlights projects implemented in three states to integrate education, health, and/or social services data in order to inform policies that influence the lives of young children and their families. The Annie E. Casey Foundation (AECF) funded KIDS COUNT organizations in the states of Mississippi (MS), Minnesota (MN), and Rhode Island (RI), supporting each state in its use of integrated data to address one pressing early childhood policy question. The Early Childhood Data Collaborative (ECDC) had the privilege of contributing to the work of the three KIDS COUNT sites by providing technical assistance to support their completion of project goals and tracking their progress to document the benefits and challenges of this work. Each site used integrated data about children from birth to age 5 to learn more about the ways young children interact with different systems. By state, the integrated data were used to learn how public assistance (MN), health (MS) and the child welfare (RI) systems intersect with and connect to early care and education (ECE) services and programs. Specifics about the three state organizations' policy questions, key findings, and recommended strategies to support the continued use of integrated data are profiled at the end of this brief.