The aim of the study was to determine and evaluate the level of sustainable development of counties in Poland. Counties were divided into four types – voivodship cities, other cities, land counties in the immediate vicinity of voivodship cities and other land counties. Statistical data from the Local Data Bank of the Central Statistical Office of Poland for 2018 were applied. A set of indicators of sustainable development was defined. Using methods of multidimensional comparative analysis, synthetic indicators of economic, social and environmental development were determined. The measure of cohesion was used to assess the level of sustainable development of counties. It enabled dividing counties into five groups: a very low, low, medium, high and very high level of sustainability. The results show that only 20% of counties in 2018 was classified as a very high level of sustainable development class. Relatively, the highest level of sustainability was observed in land counties, both those bordering large cities and other ones. It was found that the environmental aspect may be a barrier in shaping the sustainable development of counties.