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Hjarnø is an approximately 3.21 km ² large island in Horsens Fjord in Denmark. Hjarnø has 104 resident inhabitants ( 1 January 2013), of which most farmers. Hjarnø forms a separate parish municipality (Danish: Sogn ) Hjarnø Sogn, which belonged to Harde Bjerre Herred in Vejle Amt to 1970. From 1970 it belonged to Juelsminde municipality in the extended Vejle Amt and since the municipal reform of 1 January 2007 it belongs to Hedensted commune in the Region Midtjylland. Hjarnø belongs to the Association of Danish small islands. The island is accessible via a ferry from Snaptun. The journey takes about seven minutes.

The island is named after the skald Hiarne, which according to legend, in the 1st century briefly King of Denmark should have been, since he wrote the best poem on the grave late King Frode.

On the island were found in an excavation of 1935, the remains of 10 ships ratios that are between four and 13 m long and Iron Age. Ole Worm had shown more than 20 ships and stone circles in the 17th century on a sketch.