The embryonic gonad is the only organ to have a developmental choice: testis or ovary. We use the chicken as a model organism to understand these this developmental decision. In developing chicken embryos, the gonads form on the medioventral surface of the mesonephric kidneys at embryonic day (E) 3, equivalent to Hamburger and Hamilton stage (HH) 19. Before gonadal differentiation, the gonads are presumed to be bipotential and to have the same structure, cell types and gene expression profiles between sexes. At E6 (HH29), gonads begin morphological differentiation into testes in male (ZZ) embryos or unilateral ovary in female (ZW) embryos. Recently, single cell RNA-seq has been used to identify the emergence of gonadal cell types in the mouse embryo. This data focused on SF1+somatic cells and only part of development. It remains unclear whether different cell sub-populations exist, and whether there are other cell types in addition to SF1+cells. We performed single-cell RNA sequencing of entire left male and female embryonic chicken gonads at different time points: before gonadal differentiation (E4.5) and during differentiation (E6.5 and E8.5) and after somatic differentiation (E10.5). Prior, gonadal differentiation occurs the same cell populations exist in male and female gonads. The majority of the genes on each cluster were expressed equally in males and females, consistent with the previous mouse data. However, we found that female gonads have more diverse cell populations than males during development. At least nine transcriptionally distinct populations were identified the female gonads and seven in males thorough the different developmental stages post sexual differentiation. Furthermore, three cell populations were only present in male gonads and four were only present in females. These results reveal greater cellular complexity during vertebrate gonadal sex differentiation than previously thought.