Two very different kinds of models—cross-sectional models based on the logic of island biogeography and time series models of density dependence—are used to understand interest system density. While they share much in common, it is not at all clear how results derived from cross-sectional models are to be understood in terms of the temporal focus of the time series approach. Thus, the first purpose of this article is to more thoroughly think through how these two modeling strategies and their empirical findings are related to each other. We empirically assess several theoretical conjectures about the relationship of the two modeling strategies by adding a temporal element to the typical cross-sectional analysis of state interest systems via modeling density dependence pooled across four cross-sections from 1980, 1990, 1997, and 2007. By doing so, we add to the literature on state interest system density by examining how it has changed since 1980. Finally, we discuss the nature of this change and what it implies for the temporal development of state interest communities, the second focus of this analysis.