Background The term ‘long COVID’ describes ongoing symptoms and conditions experienced by people infected with SARS-CoV-2. This paper illustrates how a public health approach was used to influence and inform the development of post-COVID services across two Integrated Care Systems (ICSs). Methods A literature review was conducted between October and December 2020 to identify prevalence estimates for long COVID. The prevalence estimates were applied to locally available data on the susceptible population to estimate the number of people with long COVID. They were also used to develop a dashboard to predict fluctuations in the number of people experiencing persistent symptoms over time. Results A substantial number of people in each ICS may have experienced persistent symptoms or complications as a result of COVID-19. In Lancashire and South Cumbria, it is estimated that 33 000 people may have experienced post-COVID-19 syndrome since the beginning of the pandemic, which will include respiratory or cardiovascular complications. Conclusions The findings have been valuable in informing early service developments, engaging with managers and clinicians, and supporting applications for funding at a local level. Continued attention to emergent evidence on this topic will be vital in refining estimates and supporting service planning in the longer term.