Bill Collins - Bill is the narrator of the series. He is a red-headed freckle-faced boy, who starts the series as a 10 year old 5th grader and an only child. By the end of the series, he has aged several years and picked up a little sister named Charlotte Ann. His father is a farmer named Theodore Collins, but Bill would like to be a doctor when he grows up.
Leslie Thompson (Poetry) - Poetry is Bill's best friend, and is described as the barrel-shaped member of the gang. He has memorized so many poems, that he can recite an appropriate one in most any situation. He prides himself on his detecting abilities, and he usually has a tent pitched in his back yard.
Roy Gilbert (Dragonfly) - Dragonfly is a skinny little pop-eyed guy who is always seeing things before anyone else. Sometimes he sees things that aren't there at all, or are something else entirely. He is afflicted with a multitude of allergies and a superstitious mother.
Jim Foote (Little Jim) - Little Jim is the smallest member of the group, and he carries around a walking stick that he has carved to look like a candy cane. He has an impressive understanding of the Bible, and is an apt piano player.
Dan Browne (Circus) - Circus is so named because of his athletic ablilities. He can never resist climbing a tree or turning a cartwheel. He is blessed with a fine singing voice, but is cursed to be the only boy in a family with five sisters.
Big Jim - Big Jim is the leader of the group. He is several years older than the other guys, and they are quite envious of the fuzz on his upper lip. He grew up in another town where he was active in the Boy Scouts. He uses the skills that he learned in the Scouts to be a good leader.
Tom Till - Also known as Little Tom Till, Tom is red-haired and scrappy, much like Bill. Tom first appears with a gang of mean boys that is led by his big brother Bob. After several confrontations with the Sugar Creek Gang, Tom and Bill become friends, and Tom switches sides.