Ultracool dwarfs are the lowest-mass and lowest-temperature stars and brown dwarfs (mass M < 0.1 Msun, effective temperature Teff < 3000 K). As an abundant population with Main Sequence lifetimes that exceed the age of the Milky Way system, they are ideal tracers of the structure, formation, and evolution of the Galaxy. However, large, well-defined samples of UCDs, particularly away from the immediate Solar Neighborhood, have until recently been unavailable due to these objects’ faint magnitudes. Moreover, substellar ultracool dwarfs do not fuse Hydrogen, and cool as they age, leading to a degeneracy between mass, age, and observable properties that prevents direct inversion of the luminosity function to the mass function. Brown dwarf evolution also results in some ultracool dwarf classes (e.g., L dwarfs, T dwarfs) having different ages depending on their temperature and environment. We describe an pilot study to analyze existing deep star count and local kinematic samples using Hierarchical Bayesian modeling, and present preliminary findings on the inferred mass function, age distribution, and spatial distribution of Galactic ultracool dwarfs. We use these to make predictions of deep spectrophotometric surveys with Euclid and JWST.