The cellular census of the colonic crypt is tightly regulated, yet the molecular mechanisms that regulate this census are not fully understood. Lrig3, a transmembrane protein, is expressed in colonic crypt epithelial cells, including the stem, progenitor, and differentiated cell types. Mice missing Lrig3 have a disruption in their cellular census: using a novel Lrig3-/- mouse we demonstrate that Lrig3-/- mice have more cells per crypt, a greater mucosal area, and longer colons compared to wildtype mice, suggesting the expression of Lrig3 is required for both the total number of epithelial cells in the mouse colon, as well as colon length. In addition, we show Lrig3-/- mice have significantly more stem, progenitor, and deep crypt secretory cells, yet harbor a normal complement of enteroendocrine, Tuft, and absorptive cells. Lrig3-/- mice also have a concomitant decrease in phosphorylated Extracellular signal-related kinases, indicating the loss of Lrig3 leads to an expansion of the colonic stem cell compartment, in an Erk-dependent manner. Our study describes the expression of Lrig3 within the colon, defines perturbations in mice lacking Lrig3, and supports a role for Lrig3 in the establishment of both colonic crypt structure and cellular census, defined as the epithelial cell type and number in colon crypts.