The Czech Republic is typical for its fragmented settlement structure with a high number of small self-governing municipalities. Such a distinction causes many problems, including a non-effective way of their management. Even though various integration methods have already been applied in Europe for several decades, the Czech Republic, due to its historical development influenced by the period of communism, is still looking for intermunicipal cooperation opportunities at a higher (metropolitan) level. The presented text aims to evaluate a municipalities’ willingness to cooperate on particular activities and participate in selected topics on strategic and spatial planning at a metropolitan level. Their willingness is analysed according to the population size category of municipalities so that diverse approaches towards the willingness to cooperate could be identified for municipalities in different categories. The results are demonstrated by the example of the Brno Metropolitan Area, which is regarded to be a leader in the development of inter-municipal cooperation at a metropolitan level in the Czech Republic. The results were obtained from a questionnaire survey carried out with the mayors of the Brno metropolitan area in 2020. From a total of 184 municipalities, 175 municipalities took part in the questionnaire survey. Thus, the return was 95%. The results show that the assumption of the importance of the municipality population size is significant when making decisions about future development and cooperation within a metropolitan area. Although most municipalities in all size categories consider it useful to engage in cooperation and solve selected topics together at a metropolitan level, the municipalities in the smallest size categories of up to 1,000 inhabitants had a significantly lower proportion of very positive responses (definitely yes) than municipalities in the other categories. This fact may be attributed to the specific development of the Czech settlement system and the so-called historical memory of the residents from small municipalities during the directive merger in the 1970s and 1980s.