Once a Girl Scout, always a Girl Scout, and these stars not only served up cookies in their day ... they were exploring the outdoors and building confidence as leaders ... no wonder they're thriving today!

Scouting out the scene, celebs like Kristen Bell and Reese Witherspoon sported the heck out of their traditional uniforms ... and Dakota Fanning and Busy Philipps proudly showed off their well-earned badges!

A true cultural phenomenon, Girl Scout cookies are THE tastiest treats to exist -- bringing sweet tradition to neighbors, friends and families since 1917!

Hit up both our Girl Scout galleries and honor these leading women!

Happy National Girl Scout Day!