This article develops a framework for analysing region‐building processes as spatiotemporal constructs, involving competing spatial imaginaries and attempts at consolidating these through institution building. Central here is the performative role of what we refer to as ‘soft space imaginaries’ in the ‘phased’ building of regions for planning and economic development over time. We demonstrate how this understanding can be used to examine the phased enactment of successive waves of region‐building by tracing the evolution of multiple soft spatial imaginaries in north‐west England. The analysis exposes the variable logics, alliances of actors, and tactics used to build momentum and secure legitimacy around preferred imaginaries which advocates often promoted on the grounds that they somehow reflected ‘real geographies’ or ‘real economies’. In this context, soft space imaginaries are seen to play an integral role in intellectual case making about the contemporaneous form and purpose of subnational governance. Yet our analysis also exposes the durability of past soft space imaginaries and their continued impact on efforts to build new soft spaces. What emerges is an understanding of soft space imaginaries as more than just superficial representations. They can help determine where government investment is channelled and into what kinds of policies.