The Town of Dennis lies on the eastern banks of the Bass River, which nearly divides the cape in half. There are several small ponds and lakes in town, as well as Sesuit Harbor to the North and West Dennis Harbor to the south. The town of Dennis spans the width of Cape Cod, with Cape Cod Bay to the north, Brewster to the northeast, Harwich to the southeast, Nantucket Sound to the south, and Yarmouth to the west. The town is about 10 miles (16 km) east of Barnstable, 24 miles (39 km) east of the Sagamore Bridge, and 78 miles (126 km) southeast of Boston. The Town of Dennis comprises the villages of Dennis Port, Dennis Village (including North Dennis), East Dennis, South Dennis, and West Dennis. Dennis lies on the eastern banks of the Bass River, which nearly divides the cape in half. There are several small ponds and lakes in town, as well as Sesuit Harbor to the north and West Dennis Harbor to the south. Chapin Memorial Beach, which was previously known as Black Flats for its black sands and extensive tidal flats, was named in honor of George H. Chapin, a real estate developer who donated the land to the Town after World War II. Chase Garden Creek empties into Cape Cod Bay at Chapin Beach, and serves as a boundary between Dennis and Yarmouth. It was named for the Chase family, settlers who were on the Cape by 1638.
Currently, Dennis is a popular seaside resort town, notable for its stately colonial mansions along the northern Cape Cod Bay coastline, and its picturesque, warm-water beaches along the southern Nantucket Sound. The Cape Playhouse, in northern Dennis, is one of the oldest summer theatres in the United States (it is not clear which theatre is the oldest, as many make this claim), and among the best known. The actress Bette Davis was "discovered" while working there as an usher. Other notable past and present Dennis residents include the author Mary Higgins Clark (1927–2020) and actress Amy Jo Johnson, who grew up in Dennis.
Johnny Kelley Recreation area in South Dennis provides a hiking/jogging trail, an exercise trail, a Braille trail, playing courts and fields, playground and picnic area. The Nobscussett Conservation Area (usually called "Indian Lands") provides easy hiking trails and views along the protected shores of Bass River, where the Nobscussetts had spent their winters. Crowe's Pasture on the north side of the town provides many acres of open land and hiking with water views. Bass River Park in West Dennis offers fine views of Bass River and the boating activity there. Popular children's playgrounds are found at the Baker School in West Dennis, at the West Dennis Community Building, and at the village green in Dennis Port. The Cape Cod Rail Trail (CCRT) is a paved bikeway that runs 25 miles from South Dennis to Wellfleet. The terrain is relatively flat with some minor grades in certain sections in the Lower / Outer Cape areas, specifically Orleans and Wellfleet. It easily offers the greatest variety in scenery and natural landscapes of all the regional bike paths.