Today, cities play a crucial role as drivers of global change, as well as leaders in implementation of UN’s Sustainable Development Goals. They must capture and satisfy diverse needs of their citizens. On the other hand, e-participation adoption is crucial in open government movement as it allows the government to involve the public in their work, making it more transparent. This can be achieved through e-information, e-consultation and e-decision making as levels of e-participation adoption. This research puts focus on e-participation adoption in Croatian local governments and explores supply side of e-participation adoption with local governments’ officials. After consulting relevant literature, public sector and ICT experts, a questionnaire (i.e. measurement items) has been developed to assess e-participation levels in cities/municipalities with over 8,000 inhabitants. More than 240 responses have been collected from local governments’ heads of departments and departmental managers. The results show that the adoption of e-participation at the local level is modest with a score of 59%. E-participation sub-levels show very good adoption of e-information (e-information services widely available), mediocre results for e-consultation (mostly only compliance with respective law), and a low level of adoption of e-decision-making. The differences in adoption levels of e-participation are statistically significant between smaller and larger cities/municipalities. Therefore, the population size of the city/municipality has proven to be significant, with larger cities having higher adoption rates, especially of e-consultation practices. The author suggests a greater variety of tools and formalization of e-participation at strategic and operational levels to achieve higher levels of adoption. In addition, local governments should adopt more advanced engagement tools to enhance citizens’ (and other stakeholders’) e-participation (with voting and rating options), as current utilization is still low.