Harald Ossian Hjalmarson (14 July 1868 – 15 December 1919) was a Swedish soldier who volunteered for the Finnish Civil War in 1918 on the white army. He served as the commander of Hjalmarson's group, the Crenatorial Division, which belonged to the . At the , his actions during the war were dissatisfactory and he was not popular among the ranks. Hjalmarson received the rank of Major General in the Finnish Army, but in the Swedish Army as he was only a lieutenant colonel.