The age of the girls is rarely mentioned. They all attend Deepdale High School in the first few books and then school is never mentioned again. In volume 1, it is stated that Betty Nelson is about sixteen and that Mollie Billette is fifteen. In volume 11, Betty is eighteen and Grace Ford is "almost the same age as Betty." Mollie Billette and Amy Blackford are both seventeen in volume 11.
Betty Nelson
Betty Nelson, the daughter of a wealthy carpet manufacturer, is known as "The Little Captain" to all of her friends. Betty is the leader of the group, and it is Betty's idea to form the Camping and Tramping Club. Betty is the type of girl who always looks on the bright side of things and has the ability to make another person feel better even in the worst of situations. Betty is courageous and always knows exactly what to do in any situation, no matter how serious.
Mollie Billette
Mollie Billette is fifteen years old and is the daughter of a wealthy widow. Mollie is of French blood, and often Mollie's French ancestry is given as the reason for her unusually quick temper. Mollie angers very easily at even minor teasing, but also gets over her anger very quickly. Mollie's driving is as volatile as her temperament; she careens around curves and brakes only at the last possible moment. Mollie's brother and sister are four year old twins, Paul and Dodo, and the twins are forever getting into trouble. The twins act up on purpose and then agree to behave only if they are given candy. The twins almost always succeed in their purpose.
Grace Ford
Grace Ford is described as a typical "Gibson Girl" in appearance. Grace has blond hair and is tall and very thin, which is amazing since she is constantly eating chocolates. Grace always brings a box of chocolates with her on all of the girls' adventures or fills her pockets up with chocolates. It is quite often Grace's chocolates that Paul and Dodo covet. Grace is very lazy, and the other girls find it difficult to get her out of bed in the morning. Grace also tends to wear shoes that are inappropriate for hiking, and so often complains about her feet when the girls are walking or hiking.
Amy Blackford
Amy Stonington is the quietest and most thoughtful member of the group. Early in the series, Amy is deeply troubled when she learns that Mr. and Mrs. Stonington are not really her parents. Amy must endure the taunts of Alice Jallow, a jealous classmate at Deepdale High School, until she is finally reunited with her brother, and learns that her true name is Blackford. Amy is considered timid and sweet by the other girls, and all of them like her a great deal.
Stella Sibley
Stella Sibley enters the series in volume 14 and becomes an Outdoor Girl. Stella and her friend, Irene Moore, are described as considerably younger than the original Outdoor Girls, around thirteen years old or so. Stella is an artist and plays the piano; later, Stella becomes the leader of the Outdoor Girls after all four original Outdoor Girls have married. In volume 22, Stella successfully lands a plane with very little training after the pilot passes out, and the other girls bestow the title of "Captain" upon her since she has proved herself to be as resourceful as Betty Nelson.
Irene Moore
Irene Moore first appears in volume 14 and becomes an Outdoor Girl at the end of the book. Irene is described as being around thirteen years old. Irene is boisterous and has a talent for singing comedic songs. Irene's dog, Hesper, causes endless problems on several of the girls' outings.
Carolyn Cooper
The Outdoor Girls rescue Carolyn Cooper from a difficult situation in volume 16, and in volume 18, Carolyn becomes an Outdoor Girl. Carolyn Cooper is described as "blond and pretty and delightfully lazy."
Meg and Lota Bronson
Meg and Lota Bronson are identical twins and can only be told apart by a freckle that is on Lota's nose. Meg and Lota become Outdoor Girls in volume 18. The Bronson twins have an admirer, Dick Blossom, who cannot tell the two girls apart. The girls love to harass Dick by always dressing identically and by impersonating each other.
