Abstract Rapid technological progress and its concomitant need for new skills, ways of working and collaborating, paired with dynamic socio-economic change, have highlighted the main challenge facing Europe’s urban municipalities. Being the part of the public sector closest to citizens and their needs, the challenge addresses digital transformation’s goals to support and promote broader growth in the digital domain optimally and to realise digital transformation benefits such as user-friendly and citizen-centred services, increased quality of life and better business environments. Urban municipalities must identify local strengths, priorities and needs, including performance and digital maturity assessment, and define strategic goals and implementation roadmaps to implement digital transformation optimally. Furthermore, they must increase city administration, decision-maker and citizens awareness of the opportunities and benefits digitally enabled solutions offer. A comprehensive digital maturity self-assessment is the first step towards successful digital transformation. An example of a framework for such an assessment is the framework of the European Commission’s Intelligent Cities Challenge (ICC), the EU’s bespoke support programme for coaching, facilitation and inspiration, and successor to its Digital Cities Challenge. Therefore, the objective of our research was to analyse the digital maturity self-assessment results undertaken by eleven Slovenian urban municipalities utilising ICC’s assessment methodology framework for government services and social connectivity, which includes indicators sets of digitising public services, digital connectivity and open data. We further focused on the potential impact of municipality population size on its digital maturity. According to the existing research, this is one of the significant potential explanatory factors why municipalities differ in terms of digital transformation implementation and adaptation. One would a priori expect larger municipalities to be digitally more mature than smaller ones because they have more resources at their disposal, however, our results prove that this is not the complete picture. There is, however, a relationship between municipality population size and digital maturity, including indicators of open data sharing and security, but not entirely in the manner expected. Furthermore, our analysis has shown that municipality population size does not influence overall digital maturity but individual digital maturity indicators, highlighting the need to develop more detailed and accurate individual digital maturity indicators. Although the influence of municipality population size on overall digital maturity could not be demonstrated, its partial influence on individual sets is essential when endeavouring to achieve efficient digital transformation.