A sequential Bayesian algorithm and accompanying computer program were developed and validated to estimate population numbers of adult blacklegged tick, Ixodes scapularis Say, using mark–release–recapture methodology in field plots in central Mississippi. In fieldwork, data taken in February 2005 in a 1-ha plot yielded an estimate of 317 adult I. scapularis per ha. Data from another field plot in 2006, 3 km away, yielded an estimate of 280 adult I. scapularis per ha. The number of ticks collected per hour in both plots averaged 4.5. In eight of 14 (57%) of sampling events, the number of ticks collected per hour hovered closely around 5.0 (4.8–5.3). The computer program developed in this study readily produced statistical measures such as mean number of ticks per plot, mode, variance, and standard deviation, as well as easy-to-read graphs of estimated tick populations for each sampling period.