This study introduces new three-dimensional finite element cell modeling for simulating the structural, large deformation behavior of maturing adipocytes, based on empirically acquired geometrical properties of cultured adipocyte cells. We created models of adipocyte differentiation and maturation, which represented four stages along that process. The modeling focused on two specific and commonly used experimental setups, one involving compression of individual adipocytes and the other stretching of adipocytes. Both are physiological loading regimes for fat tissues and cells in vivo, and both are often employed for testing cell responses to deformations in the context of obesity and pressure ulcer research. In both simulation types, and in all the cell models, external loads induced localized effective Lagrange strains in the plasma membrane that reached maximum values over the lipid droplets (LDs). We also observed that the effective stresses (averaged across the entire cell volume in each model case) increased with cell maturation and varied between cells with different structure and dimensions. This result points to an increase in the effective cell stiffness with maturation, which would have been expected, since the volume of the stiffer LDs increases as adipocytes mature. Overall, the mechanical behavior of an individual cell is influenced not only by the external mechanical loads that are exerted, but also by the cell structure and dimensions, and is fundamental to any interpretation of cell mechanics experiments, and particularly for testing adipocytes.