Louth Island (Nauo: Jorunu or Yoruna) is a 135 ha island located in Louth Bay, Spencer Gulf, South Australia. The island is privately owned, and has previously been used for the grazing of sheep and mining of guano. The island has an old building with sleeping quarters, several beaches, inshore rocky reef and a boat anchorage. It is 17.5 km NNE of Port Lincoln and is easily accessible by boat. The indigenous name for the island is Yorunu.

In January 1861, a sheep which had been grazing on Louth Island for three years demonstrated remarkable growth of wool. One sample showed a staple twelve inches long, and its fleece was said to have weighed 24 lbs. At the time, the island and its stock were in the custody of Captain Bishop of Port Lincoln.

In the late 1800s, Louth Island was in the custody of Alexander Watherston.

In the early 1900s, waters around Louth Island were dredged for oysters.

On October 13, 1905, William Watherstone, lessee of the island, died in Port Lincoln. He was 49 years of age and suffered from Bright's disease and complications. He was one of the region's oldest residents, having arrived in 1859.

In 1910, it took three shearers on Louth Island a fortnight to shear 800 sheep due to bad weather.

In 1915, Louth Island was purchased at auction by W. B. White of Port Lincoln. The price paid was £4 8/6 per acre.

In 1917, a lease was offered at auction to permit the removal of guano from the coastal reserve surrounding Louth Island.