<p>This study investigates the spatial and temporal dynamics of population distribution in the Chinese mainland from 1953 to 2020, using county-level data from seven national censuses. Integrating spatial analysis with time-series forecasting, it examines trends at national, regional, and county scales to assess migration patterns, concentration effects, and regional divergence. Results show that although the total population of the Chinese mainland increased over the past seven decades, the spatial pattern of dense settlement in the southeast and sparse settlement in the northwest, demarcated by the Hu Line, remained largely stable. The population centroid showed an overall southward shift, driven by eastern growth and northeastern decline, with eastern coastal agglomerations intensifying. Projections indicate population peaking at around 2020 and then declining to about 1.396 billion by 2030, alongside widening regional disparities: sustained growth in the eastern, stability in the central, modest gains in the western, and continued losses in the northeastern. The internal distribution has shifted from “multi-polar dispersion” to “coastal polarization”, producing a pattern of “southern growth, eastern concentration, western sparsity and northern decline”. These trends highlight the urgent need for region-specific policies to manage demographic decline and promote high-quality and balanced population development.</p>