The article observes specific features of formation of united local communities in Ukraine according to the principle of economic efficiency. Influence of amount of population and area of united territorial community on its financial situation and ability to perform its functions is analyzed. Main features of management and administrative staff of united communities of all volumes are established. It is defined inversely proportional dependence between the level of expenditures per pupil and volume of the community. It means that expenses on pupils at small communities are greater than at big communities. It is proposed a matrix to determine optimal parameters for united municipalities formation. The basic actions that state should realize for effective implementation of the reform of fiscal decentralization are defined. It is proved that formation of united local communities, that can be characterized with optimal features, which are defined at the article, will facilitate effective development of communities and provision of quality public services to their residents.