Rebecca Lipscombe and Evelyn Miles joined West Midlands Police in April 1917, the first women to do so.
By 1919 the force had 11 female officers, though no more were recruited until 1931.
Three of the officers in an archived picture of the unit remain unidentified and now the force is asking for help from the public.
West Midlands Police said files on four officers - Elsie Chapman, Mary Dwelly, Lizzie May Peers and Malenda Shawe - have not survived.
Corinne Brazier, who has worked with Insp Steve Rice on a book to mark the centenary of the force's first female officers, said they have been "unable to match names with faces" and would "love to complete the picture".
"These women paved the way for the many female officers we see in the force today," she said.
"I'd love to hear from anyone who believes they may be descendants of our pioneering WPCs or anyone who has old photographs or information on our early police women."
A police force is appealing for information on some of the first female police officers it recruited.