We report on the shear modulus G of colloidal crystals formed from thoroughly deionized suspensions of charged latex spheres. G is measured as a function of particle number density n. Body-and face-centered-cubic (bcc and fee) crystal structures are observed by simultaneously performed static light scattering, and a broad coexistence region is found between (2.7+/-0.1) x 10(18) m(-3)less than or equal to n less than or equal to(4.8+/-0.2)x 10(18) m(-3). Below n-10(19) m(-3), G closely follows theoretical predictions for both bcc and fee, while it stays constant throughout the transition region. Above 10(19) m(-3), G still observes the predicted n-dependence but with values larger than expected. While in that region, an upper bound of particles per crystallite is estimated from scattering data to be on the order of 10(4); the abrupt change in G cannot be solely attributed to the gradual morphological transition from polycrystalline to nanocrystalline materials.