<p>Working memory and evidence integration are fundamental components of cognition. Theoretical and behavioral studies argue that both processes are required for plume navigation, a behavior in which animals use stochastic sensory cues to navigate towards an odor source. Here we identify a small population of local neurons in the navigation center of <i>Drosophila</i> that exhibits both theorized processes. During virtual plume navigation, a bump of activity in this population ramps up with successive odor encounters, and can persist for variable intervals after odor loss. While the bump persists, the fly maintains the goal heading it adopted during odor. Silencing these neurons impairs this persistence. Simulations show that the time constant of persistence observed in these neurons optimizes navigation in a turbulent boundary layer plume. Our work localizes working memory and evidence integration to a specific group of neurons, which will facilitate the mechanistic dissection of these building blocks of cognition.</p>