The Hokianga is in the Far North District, which is in the Northland Region, and is 120 kilometres northwest of Whangarei and 40 kilometres west of Kaikohe by road. The estuary extends inland for 30 kilometres from the Tasman Sea. It is navigable for small craft for much of its length, although there is a bar across the mouth.
Twelve thousand years ago Hokianga was a river valley flanked by steep bush-clad hills. As the last ice age regressed, the dramatic rise in sea level slowly flooded the valley turning it into a tidal, saltwater, harbour with abundant sheltered deep water anchorages. This was the harbour that Kupe left from, and in 1822 saw the first European timber entrepreneurs. Southern Right Whales possibly frequented in the bay historically prior to significant depletion of the species caused by commercial and illegal hunts including mass illegal slaughters by Soviet Union with helps from Japan in 1960s to 80s. Today, large whales are rarely seen in the bay while smaller dolphins and Killer Whales are more common in the harbor water, as the harbour is one of well-regarded areas to watch them from shores.
The area around the harbour is divided in three by the estuary. To the south are the settlements of Waimamaku, Omapere, Opononi, Pakanae, Koutu, Whirinaki, Rawene, Waima, and Taheke; to the north are Broadwood, Pawarenga, Panguru, Mitimiti, and Rangi Point; and at the top of the harbour upstream from the narrows are Horeke, Kohukohu and Mangamuka.