Somersby is a semi-rural locality of the Central Coast region of New South Wales, Australia, to the northwest of Gosford along the Pacific Highway. It is part of the Central Coast Council local government area.

Somersby includes sections of the Brisbane Water National Park, within which Somersby Falls are located, as well as the Mount Penang Parklands which are used as a festival and exhibition centre. The Woolshed Function Centre, Australian Reptile Park, a small industrial area near the Kariong Interchange, two juvenile justice centres, and a primary school are features of Somersby. Old Sydney Town, now defunct, was a popular tourist destination in Somersby.

Somersby has a number of heritage-listed sites, including:

• Pacific Highway: Mount Penang Juvenile Justice Centre

St Francis of Assisi Catholic Church

• 
  View north up the upper Somersby Falls
• 
  One of several sets of Aboriginal rubbing groves at the upper Somersby Falls
• 
  View across the upper Somersby Falls
• 
  View west down from the upper Somersby Falls

• Holt-Bragg Bridge

33°21′54″S 151°17′06″E / 33.365°S 151.285°E / -33.365; 151.285