Population Changes and Spatial Segregation Dynamics in Southern European Urban Areas: The Case of Messina

European countries have experienced significant transformations in their urban populations, with a resurgence of the residential segregation challenges. Yet, empirical analyses focusing on spatial dynamics within urban areas and between the main urban places, along with the changes in demographic profiles of populations, remain rare. The study examines segregation patterns within the area of Messina, Italy—an archetypal city in the Southern European region. To quantify segregation, Theil's H index and Shapley decomposition are employed, capturing entropy at both the micro and macro levels. At the micro level, analysis is conducted using census sections, while at the macro level, two aggregation schemes are utilised: a historical and administrative classification based on municipal districts and a functional classification organised along an urban‐to‐extra‐urban gradient. Results highlight a dual framework of segregation between and within each spatial category (macro‐micro level). Notably, the decline of the Italian population in central areas exacerbates macro‐level segregation, particularly for migrant populations, such as Sri Lankans and Moroccans, while contrasting dynamics emerge for Romanians and Filipinos. Findings uncover the critical role of socio‐economic disparities in shaping segregation patterns. Although hosting the majority of migrants, central districts exhibit mixed signals of desegregation, coherent with housing market exclusion and population turnover. Peripheral zones, conversely, remain marked by demographic stagnation and limited integration opportunities. By contextualising these patterns within broader theoretical models of spatial assimilation and stratification, this research contributes to the literature underscoring the nuanced interplay of demographic shifts and urban segregation dynamics.