RhoPop identifies compositionally distinct populations of small planets (R≲2R_⊕). It employs mixture models in a hierarchical framework and the dynesty (ascl:1809.013) nested sampler for parameter and evidence estimates. RhoPop includes a density-mass grid of water-rich compositions from water mass fraction (WMF) 0-1.0 and a grid of volatile-free rocky compositions over a core mass fraction (CMF) range of 0.006-0.95. Both grids were calculated using the ExoPlex mass-radius-composition calculator (ascl:2404.029).