Final answer:
About 15 percent of the world's population is categorized as nonreligious, with the highest concentrations typically found in developed and secularized countries such as those in Europe.
Step-by-step explanation:
Approximately 15 percent of the world's population is categorized as nonreligious. The prevalence of nonreligious people is highest in regions where secularization has taken a strong hold, particularly some developed countries. In Europe, for instance, many people identify as Christians but the level of active participation and commitment to their faith can be quite low, indicating a greater degree of secularization. Similarly, despite being a religious country when compared to others in the economically advanced world, the United States also has a significant portion of individuals who are nonreligious. The exact country with the highest percentage of nonreligious individuals can vary as secular trends continue to change the religious landscape.