Question: This town with a population of 2,216 as of 2010 is home to a fortification at the mouth of what river?

Context paragraphs:
Newbury (town), Vermont: Newbury is a town in Orange County, Vermont, United States.  The population was 2,216 at the 2010 census.  Newbury includes the villages of Newbury, Center Newbury, West Newbury, South Newbury, Boltonville, Peach Four Corners, and Wells River.  The town maintains a public website that is updated regularly.

Farmer's Castle: Farmer's Castle was a defensive fortification built opposite the mouth of the Little Kanawha River on the Ohio River by a group of pioneers from the Ohio Company of Associates.  It was located about 15 miles downriver of Marietta, Ohio, the first European-American settlement in the Northwest Territory.  The pioneers had surveyed the land during the winter of 1788-89, and moved from Marietta to their new farms in April 1789.  They called their town Belle-prairie, or modern day Belpre, Ohio.  Adjacent to the island later known as Blennerhasset Island, the settlers began construction of Farmer’s Castle during January 1791 for protection during the Northwest Indian War.

River Heads, Queensland: River Heads is a town in Queensland, Australia, 18 km south of the city of Hervey Bay.  The town is built on a narrow peninsula surrounded by the Great Sandy Strait (to the east), the mouth of the Mary River (south) and the mouth of the Susan River (a tributary of the Mary) to the west.  At the 2011 census , River Heads had a population of 1,294.

Mimika Regency: Mimika Regency is one of the regencies ("kabupaten") in Papua province, Indonesia.  It covers an area of 21,633 km, and had a population of 182,001 at the 2010 Census; the latest official estimate (as at January 2014) is 223,949.  The administrative centre is the town of Timika, which lies within Mimika Baru District, which has 118,100 inhabitants (in 2010) within 2,216 km.

Fort Knox (Maine): Fort Knox, now Fort Knox State Park or Fort Knox State Historic Site, is located on the western bank of the Penobscot River in the town of Prospect, Maine, about 5 mi from the mouth of the river.  Built between 1844 and 1869, it was the first fort in Maine built entirely of granite; most previous forts used wood, earth, and stone.  It is named after Major General Henry Knox, the first U.S. Secretary of War and Commander of Artillery during the American Revolutionary War, who at the end of his life lived not far away in Thomaston.  The fort was designated a National Historic Landmark in 1970, as a virtually intact example of a mid-19th century granite coastal fortification.  Fort Knox also serves as the entry site for the observation tower of the Penobscot Narrows Bridge that opened to the public on 19 May 2007.

Little River, California: Little River (also known as Littleriver, Bells Harbor, and Kents Landing) is a small census-designated place in Mendocino County, California.  It lies at an elevation of 66 feet (20 m).  It is located two miles (3 km) south of the town of Mendocino and running along the Pacific Ocean coast on State Route 1.  The town is home to several hundred people and takes its name from nearby Little River.  The town center sits on a scenic bluff overlooking the mouth of Little River and hosts a grocery store, two gas pumps, a post office, and a restaurant within a single structure.  The population was 117 at the 2010 census.

Carbondale, Colorado: The Town of Carbondale is a Home Rule Municipality in Garfield County, Colorado, United States.  The town population was 6427 at the 2010 United States Census.  The town is located in the Roaring Fork Valley, downstream from Aspen and upstream from the mouth of the Roaring Fork River at Glenwood Springs.  The town proper sits on the south bank of the river, at the confluence of the Crystal River.  Carbondale's horizon is dominated by the 12,953 ft (3,952 m) tall Mount Sopris several miles to the south of town.

Naryan-Mar: Naryan-Mar (Russian: Нарья́н-Мар ; Nenets: Няръянa марˮ, "Nyar'yana marq", literally "red town") is a sea and river port town and the administrative center of Nenets Autonomous Okrug, Russia.  The town is situated on the right bank of the Pechora River, 110 km upstream from the river's mouth, on the Barents Sea.  Naryan-Mar lies north of the Arctic Circle.  Population:  (2010 Census) ;  (2002 Census) ;  (1989 Census) ; 17,000 (1973).

Fort Popham: Fort Popham is a Civil War-era coastal defense fortification at the mouth of the Kennebec River in Phippsburg, Maine.  It is located in sight of the short-lived Popham Colony and, like the colony, named for George Popham, the colony's leader.

Phippsburg, Maine: Phippsburg is a town in Sagadahoc County, Maine, United States, on the west side of the mouth of the Kennebec River.  The population was 2,216 at the 2010 census.  It is within the Portland–South Portland–Biddeford, Maine, metropolitan statistical area.  A tourist destination, Phippsburg is home to Bates-Morse Mountain Conservation Area, Fort Popham State Historic Site; it is also home to Fort Baldwin which overlooks Fort Popham, and Popham Beach State Park, as well as Pond Island National Wildlife Refuge.  The town includes part of Winnegance.

Supporting paragraphs: Phippsburg, Maine Fort Popham
Answer: Kennebec River