In this paper, we address two significant empirical and theoretical gaps in two literatures. The first is documenting how a data ecosystem emerges and evolves as a socio-technical assemblage over a substantive period of time. To date, studies of data ecosystems have examined their organization and operation at a particular point in time, but have not empirically detailed how they are constructed, maintained and change over time. The second is charting the digitalization of a planning data ecosystem as it transfers from a paper-based endeavour to one that is digitally mediated. While a number of studies have examined the adoption and use of specific digital technologies in planning, there has been no detailed examination of the suite of digital technologies that have been assembled for undertaking the day-to-day work of planning development and control (the management of the planning and construction pipeline from planning application, to appeals process, to building control). We resolve these two lacunae through a genealogical analysis of the digitalisation of the development and control function of planning and its associated data ecosystem in Ireland over a 25 year period. Our analysis reveals the contingent and relational nature of (planning) data ecosystems and the social, political and technical work that continually reconfigures their relations and practices.