Jack Harkness's mother lived on the Boeshane Peninsula with her husband and her two sons, Jack and Gray.
Following the attack by the "worst creatures in existence," she and Jack were the only survivors in their family; Gray was captured after Jack accidentally let go of his hand, and Franklin was killed by the creatures, with Jack returning home to find his mother cradling Franklin's corpse. (TV: Adam)
Jack later implied in a conversation with Esther Drummond that he did not know what had happened to his mother, suggesting that she was still alive when he left his time frame. (TV: The Categories of Life)