An unknown population of Medionidus simpsonianus (Ochlockonee Moccasinshell) was discovered in the lower Ochlockonee River downstream of Jackson Bluff Dam in 2014. This discovery confirms that the species is extant, extends its known range by nearly 100 rkm, and represents only the second known collection of this species in the lower Ochlockonee River Basin. Ochlockonee Moccasinshell is endemic to the Ochlockonee River Basin (ORB) in Florida and Georgia. It was historically known from 9 locations in the upper ORB upstream of Lake Talquin and from 1 record in the lower ORB downstream of Jackson Bluff Dam. Collections of Ochlockonee Moccasinshell decrease in regularity after 1950, and the last record of a live individual was 1995. We surveyed 55 sites downstream of Jackson Bluff Dam in a reach of river having received little effort in the last 20 years. We employed visual/tactile searches using mask and snorkel from shore to a depth of 2.5 m and found 22 live individuals of Ochlockonee Moccasinshell at 9 locations from 47–65 river km (rkm) downstream of Jackson Bluff Dam. Further survey effort is needed to update the status and range of Ochlockonee Moccasinshell and other freshwater mussel populations of the lower ORB.