Relaxor ferroelectrics are materials exhibiting dielectric dispersions in their maximum permittivity temperature without macroscopic phase transition into a ferroelectric state. Their exceptional properties are exploited in a variety of dielectric and piezoelectric applications. As it is generally believed that polar nanoregions play a crucial role in relaxor behavior, there are great interests in exploring how the atomic structures affect the relaxor properties. Here, using the dark field imaging and atomic-resolution electron microscopy, we investigate the nano and atomic structure of a lead-free ferroelectric-relaxor Ba(Ti1−xSnx)O3 system at high temperature. The local atom displacements and their spatial correlations are measured, and the atomic structure of static polar nanoregions in the relaxors is reported. For the materials exhibiting normal ferroelectricity, no such static polar structures can be seen. Based on our experimental observations, we suggest the static polar nanoregions are responsible for the relaxor behavior in this lead-free system.