From the episode "Wildfire"
As Jim helps in the cleanup of zombie corpses the morning after the attack, Jacqui notices blood on his shirt, and demands he lifts up his shirt, but he rejects so she alerts the remaining survivors. T-Dog restrains him, and Daryl lifts his shirt to reveal the bite wound he suffered during the attack on the camp. There is controversy over Jim as the survivors discuss what to do. Daryl wants to kill him immediately, but is stopped by Rick. Jim is taken with the rest of the survivors in the RV as the women care for him as he throws up and burns from a fever. While on the road, he complains of his sickness and asks that he be left behind, for the sake of the survivors. He is left by a tree, after refusing to take a handgun from Rick, and is bid farewell by each of the survivors as they leave.
His fate is left unknown, but presumably, he succumbed to the fever, reanimated, and is now a walker.