Research Objective: The Affordable Care Act created new incentives for hospitals, insurers, employers, public health agencies, and others to contribute to activities designed to promote health and prevent disease an injury, potentially changing the structure of public health delivery systems and expanding the delivery of strategies that improve population health. At the same time, the economic recession has constrained government and private sector spending on health and health care, necessitating changes in the scope and scale of public health delivery. This study uses data from the 1998-2012 National Longitudinal Survey of Public Health Systems to examine: (1) the extent and nature of change in inter-organizational contributions to public health activities, with a focus on hospitals, insurers, employers, and primary care providers; and (2) the degree to which selected organizations attenuate or accentuate changes made by peer organizations in public health contributions, using estimates of inter-organizational complementarities, substitution effects, and network effects. Study Design: Our retrospective cohort design follows more than 350 U.S. communities over time using survey data collected initially in 1998 and again in 2006 and 2012. The surveys ask local public health officials to report on the availability of 20 recommended public health activities in the community, which organizations contribute to each activity, and perceptions of how well each activity is performed. We construct measures of the scope of public health activities contributed by each type of organization in each community and year, along with network analytic measures of organizational influence (density and centrality) within the local public health delivery network. Generalized estimating equations and dynamic structural equation models are used to estimate complementarity effects, substitution effects, and network effects for each type of organization. Population Studied: A total of 354 communities containing 100,000 or more residents in 1998, representing more than 70% of the total U.S. population. A sample of 50 smaller communities was included in 2006. Principal Findings: The proportion of recommended public health activities delivered in the average community increased from 64% in 1998 to 70% in 2006, but fell back to 67% in 2012. More than three-quarters of communities experienced reductions in the scope of public health activities delivered between 2006 and 2012. Public health contributions by state and local government agencies and employers decreased steeply during this period (41%, 21%, and 21% reductions), while hospital and health insurer contributions declined by much smaller margins of 4.5% and 2.5%, respectively. Multivariate estimates show that hospital and health insurer contributions helped to attenuate the impact of government agency reductions in public health delivery through substitution effects, while physician practices and employers accentuated government reductions due to complementarities. The magnitude of these effects varied with organizational centrality within the local network. Conclusions: Health system stakeholders respond differently to policy incentives and economic constraints that shape public health delivery. Private-sector contributions to public health appear to offset governmental reductions under certain organizational and community conditions. Implications: Methods to model the interorganizational dynamics of public health delivery can help stakeholders anticipate and respond to policy and economic change.