•An analytical framework is developed to predict the elastic properties of irregular auxetic structures.•A finite element code is developed to validate the analytical predictions.•The effects of the degree of irregularity and geometric parameters on the elastic properties are investigated. This paper presents an analytical framework with a bottom-up multi-step approach to predict the in-plane mechanical properties including the effective Young’s modulus and Poisson’s ratio in two directions. There are deviations for the analytical predictions with respect to the numerical results because of the simplifications of boundary conditions of the representative unit cell. To remedy the deviations, a modification coefficient is embedded to revise the analytical model. A finite element code for obtaining elastic properties of the irregular auxetic structures is developed to validate the revised analytical model. The good agreement between the revised analytical predictions and numerical results affirms the accuracy of the revised analytical model. It is noticeable that the effects of irregularity on the effective Young’s modulus are more prominent than on the Poisson’s ratio.