Farmers’ entrepreneurship in Poland has both a historical and economic basis and stems from personality traits. It is supported by national and EU projects and funding. Legal conditions also favor farmers’ entrepreneurial activity. The aim of the article was to analyze the influence of selected factors on the development of entrepreneurship among farmers in Siedlce County (with a high percentage of employment in the agricultural sector), measured by the entrepreneurship index in 2012 and 2022, and to find out which factors had the greatest impact on its development over the course of ten years. The research material consisted of data from thirteen municipalities of Siedlce County as at the end of 2012 and 2022, from Statistics Poland, and municipal offices, as well as the results of surveys in which respondents assessed the change in entrepreneurship development conditions in 2022 compared to 2012. The dependence of the entrepreneurship index on selected variables was assessed using the simple correlation coefficient and multiple linear regression equations. The econometric analysis showed that the entrepreneurship index in both 2012 and 2022 in the municipalities of Siedlce County was shaped by: the number of national economy entities, the share of annual own income per capita, and the share of agricultural tax in the municipalities’ own income. The respondents assessed that during the period under study, the share of non-agricultural income in total income increased, while the income situation worsened in relation to 2012 and there was a decrease in income from non-agricultural activities against the income of other occupational groups. Factors that significantly affected the entrepreneurship rate were shown to have changed in the decade under analysis. The overall situation shaping entrepreneurial development has also deteriorated.