This study was motivated by the profound disparity of farmers’ income in northern Thailand. We aimed to investigate the inequalities in the distribution of estimated income among urban farmers in the Mueang district area of Nan province using the Lorenz curves and Gini indices. Approximations of farmers’ incomes were calculated and the Tobit model was applied to identify the determinants of farm income diversification in each sub-district. Results showed that urban farmers had high inequality scores, and there was a wide range of income among farmers. Ownership, land entitlement, and farmland size positively contributed to farmers’ estimated income. Agricultural activities further showed that rice farming significantly raised income disparity, while maize cultivation negatively affected it in nearly all sub-districts. Therefore, this study contributes an important indication that leads farmers to a sustainable livelihood while simultaneously adjusting relevant institutional policies.