Consistent with the storylines, the cast of Carol Day derives mainly from her love life, her work, her family, and the life of the village where her Uncle Marcus lives. There is a regular, recurring supporting cast of characters who are usually not at the center of the plot, for example Carol's uncle and guardian Marcus Axel and his butler Baines.

Other characters recur at the center of more than one story. We get to see how their lives and characters have developed (often for the worse) since they initially intersected with Carol, and this adds a richness to the strip. For example, Oswald Patcham, first introduced in Last of the Line returns in a later story in which he is being conned by Julius Grivo. Charles Logan, Carol's long-time suitor, is a more complex example, and his difficult relationship with Carol forms the basis of several excellent stories.

This guide to the cast provides a brief introduction to the main characters so that you can quickly place an unfamiliar face or see what other stories a main character has appeared in. The guide is organized alphabetically by first name. Additional reference information about the characters will be filled in over time.