Mitchells Island is the largest of several islands in the mouth of the Manning River. It is roughly triangular in shape and has an area of approximately 130 km (50 sq mi). It is bordered on the north by the main channel of the Manning River, on the southwest by Scotts Creek, and on the east by the Pacific Ocean. The ocean edge extends from Old Bar in the south to Harrington to the north.

Mitchells Island is located at 31°53'60S 152°37'0E and varies its altitude from sea level to 151 m (495 ft). It is named after Thomas Livingstone Mitchell (1792–1855), who served as Surveyor-General for Australia. It and the adjacent Oxley Island is a shale outcrop rather than a sandy deposit.

The population of Mitchells Island is approximately 300 permanent residents. Much of the island was covered by dairy farms but today there is only one remaining farm. It is a popular holiday location and has two caravan parks and many rental homes and units.

Mitchells Island largely consists of dense rainforest, home to many native animals including koalas, echidnas, wallabies, possums, bandicoots, quolls, goannas and birds.

The housing estate Manning Waters was developed in 1991 with two houses, growing to 36 homes today. The Island's historical St. Marks church was built in 1872, its first service on 6 June of that year. Legend has it the Church was built from a large cedar log washed down river from the timber mill during floods, and the cemetery is on the highest point of the Island looking over the river towards the little brother mountain ranges. There is one village on the island, Manning Point, approximately 330 km (210 mi) north of Sydney. Besides the holiday rental units, it has a general store, a bowling club, the two caravan parks, a cafe, and a bait shop. The general store is also the news agent, the video rental shop, the Australia Post Office, the bottle shop, the burger and fish and chips grill, and the grocery store.

The Pacific Ocean forms the eastern border of the island. While the entire length is a sand beach, there are two accesses. The northern access is from the village of Manning Point and is reinforced to allow four-wheel drive vehicle access. The southern access is from Beach Road and has no vehicular access and is pedestrian access only. This access is blocked to vehicles and is a narrow pedestrian path over the boundary dune. Neither beach is patrolled.

31°54′S 152°37′E / 31.900°S 152.617°E / -31.900; 152.617