Aquatic beetles in the families Dryopidae, Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Hydrophilidae, Noteridae, Psephenidae, and Scirtidae were sampled at the Ravenna Training and Logistics (RTLS) site in northeast Ohio from 1999 through 2001. The site is a military base with restricted access, but military activities can cause considerable environmental disturbance. The RTLS has many headwater streams that are part of the Mahoning River basin. It is therefore an important resource in maintaining stream quality in this watershed. This survey is the first comprehensive effort at surveying the aquatic beetles at the RTLS. 124 species were collected including three haliplids, three dytiscids, one gyrinid, and three hydrophilids that were new state records for Ohio. We used these capture data to obtain preliminary estimates of biodiversity in different portions of the RTLS, and estimate how many species we missed in our sampling program. We estimated that about 90% of the total species present at the RTLS were recovered in this survey.