Movement and longevity studies inform management and conservation plans for imperiled organisms. We used a mark–recapture study to reveal information about these key biological characteristics for imperiled Okaloosa Darters (Etheostoma okaloosae). Okaloosa Darters were captured from 20 m reaches at six separate streams, marked with VIE on the left or right dorsum according to the side of the stream from which they were captured, and released on the same side where they were captured. Okaloosa Darters were recounted (but not recaptured) at 24 h and one month, and then recaptured once per year for the following eight years. During the final recapture year, we measured standard length of all Okaloosa Darters and constructed length frequency distributions to identify distinct cohorts. We found that significant numbers of Okaloosa Darters remained within their 20 m reaches after 24 h (31%), one month (45%), and one year (22%) and rarely crossed open, sandy stream channels from one side to the other. Our recapture data and length frequency distributions indicate that Okaloosa Darters live longer than the 2–3 years suggested by previous authors. One of our recaptured fish was at least eight years old, making Okaloosa Darters the most long-lived etheostomine.