Purpose: The aim of this study is to assess and discuss the relationship between the financial situation and the level of socio-economic development of coastal rural and urban-rural municipalities in Poland. Approach/Methodology/Design: The diversity of coastal municipalities in Poland due to the level of socio-economic development and financial situation was examined using a synthetic indicator. The analysis was carried out on the basis of data from the Local Data Bank of the Central Statistical Office and from the Ministry of Finance and Regional Accounting Chambers. The time range covers 2004-2017. Findings: The analysis shows that there was a statistically significant and bilateral relationship between the financial situation and the socio-economic development in Polish coastal municipalities in the years 2004-2017. Moreover, the results of an extensive analysis of this relationship showed that despite the fact that a statistical relationship was found in the analyzed period, such a relationship was not proven for each class and each municipality. In the case of the study taking into account classes of different levels, a significant relationship did not occur in the extreme classes, but only in the average. Practical Implications: The conclusions refer to the assumptions of the regional and local policy. Originality/Value: The study concerns current issues of regional and local policy. The results can contribute to the analysis of creating development at the local level.