Little Harbor and Sandy Beach are two popular destinations in Cohasset. Little Harbor is a scenic inlet that offers a variety of recreational activities, such as kayaking, fishing, and birdwatching. Sandy Beach is a public beach that features soft sand, clear water, and lifeguards.

Cohasset has a total area of 31.4 square miles, It is bordered on the west by Hingham, on the northwest by Hull, on the north and northeast by Massachusetts Bay, and on the east and south by Scituate. Cohasset is approximately 12 miles east of Braintree and 20 miles by road southeast of Boston.

Cohasset is located on the "corner" of the South Shore, where greater Boston Harbor ends and Massachusetts Bay begins. The shore is rocky, with many small ledges and rocks lying offshore. Cohasset Cove and The Gulf provide a long portion of the border with Scituate, while Straits Pond divides Cohasset from neighboring Hull. Near the center of the coast lies Little Harbor, a large inlet divided from the ocean by Beach Island. Several other brooks and rivers run through the town. A large portion of the southwestern part of town is occupied by Wompatuck State Park (formerly the Hingham Naval Ammunition Depot Annex), and the Whitney and Thayer Woods Reservation. There is also a bird sanctuary, as well as a large park (Wheelwright Park) near Little Harbor. There are three beaches along the bay, the Cohasset Yacht Club, Cohasset Sailing Club, and a public boat launch in Cohasset Harbor.