John Cusacke (died 1626) was a wealthy merchant, landowner and local politician in seventeenth-century Dublin, who served as both Mayor and Sheriff of Dublin city. He was born in County Meath, eldest of the ten children of Patrick Cusacke of Ballymolghan and his wife Maud Plunkett, daughter of Thomas Plunkett of Loch Gabhair (Lagore), Ratoath. The Cusacks were recorded at Ballymolghan from 1508. He was admitted as a freeman of the city of Dublin in 1592, having served his apprenticeship. He married Margaret Allen, daughter of Giles Allen, a former Mayor of Dublin, and widow of John Gough, an alderman of Dublin. They had five children, including Robert, who inherited his father's estate and sat in the Irish House of Commons as MP for Kells in 1640–42, and Anne, who married Richard Barry.