Havre de Grace, abbreviated HdG, is a city in Harford County, Maryland, United States. It is situated at the mouth of the Susquehanna River a…Havre de Grace, abbreviated HdG, is a city in Harford County, Maryland, United States. It is situated at the mouth of the Susquehanna River and the head of Chesapeake Bay. It is named after the port city of Le Havre, France, which in full was once Le Havre de Grâce.