Objective To measure the palatal thickness of both hard and soft tissues and to determine safe regions for the placement of mini-implants. The influences of sex and age on palatal thickness were also examined. Materials and Methods Cone-beam computed tomography images of 30 patients (12 males, 18 females), including 15 adults and 15 adolescents, were used in this study. The thicknesses of palatal hard tissue, soft tissue, and hard+soft tissues were measured at the coronal planes of first premolars, second premolars, first molars, and second molars (P1, P2, M1, and M2 planes, respectively). Results The hard tissue was thickest at the P1 plane, followed by at the P2, M1, and M2 planes, while the thickness of soft tissue was similar among the four planes. The trends in the changes of palatal thickness from midline to the lateral sides (V-pattern) were similar for the four planes. Palatal thickness was influenced by sex, age, and their interaction. Mapping of recommended and optimal sites for palatal mini-implants was accomplished. Conclusions Sex and age factors could influence palatal thickness. Therefore, the findings might be helpful for clinicians in guiding them to choose the optimal sites for palatal mini-implants.