A liquid holding unit supplies liquid to a liquid ejector of a liquid ejection device. The liquid holding unit includes a liquid holder, an inlet, a plug, a shaft, and an engagement portion. The liquid holder holds the liquid. The housing accommodates the liquid holder. The inlet is used to fill the liquid holder with the liquid. The plug opens and closes the inlet and includes an elastically deformable plug body that covers the inlet and a holding member that holds the plug body and has higher rigidity than the plug body. The shaft is arranged on one of the housing and the plug. The plug is pivotal about the shaft. The engagement portion arranged on the other one of the housing and the plug and engaged with the shaft.