Endogenous growth theory has not yet consistently incorporated population growth or immigration into its models. As a result, in the present day, there is no universally accepted endogenous growth model explaining the empirical observed relationships between growth, population and immigration. The present paper overcomes this inconvenience by designing a fully specified Romer endogenous growth model, completely microfounded, that incorporates the existence of population growth and immigration and that allows the stylized facts of growth as well as the relationships between growth, population and immigration to be explained. In addition, the proposed model is susceptible to calibration and simulation, and, when applied to the US economy, provides a good fit to the data.