Question: Contoocook River has a bridge that is in the town in what New Hampshire county?

Context paragraphs:
Contoocook Mills Industrial District: The Contoocook Mills Industrial District of Hillsborough, New Hampshire, encompasses the industrial mill complex of the Contoocook Mills, a major business in the town from the 19th century to the mid-20th century.  Industry on the banks of the Contoocook River in Hillsborough began as early as 1763, when a sawmill and gristmill were operated in the area.  More modern industrial activity began in 1828 with the construction of a cotton mill by Josiah Marcy.  This three story timber frame building stands on the south side of Mill Street, on a granite foundation through which a raceway provide the water which powered the mill.  Marcy expanded his operations, building a grist mill and saw mill before his death in 1848.  The grist mmill, a handsome brick building on the north side of Mill Street, was operated as such until 1884, after which it was converted into the picker building for the main mill complex.

Hancock-Greenfield Bridge: The Hancock-Greenfield Bridge is a historic covered bridge carrying Forest Road over the Contoocook River at the town line between Hancock and Greenfield, New Hampshire.  The New Hampshire Department of Transportation covered bridge database refers to it as County Bridge.  It is a single-span Teco-Pratt timber truss, 88 ft long and 27 ft wide, with an internal clearance of 14 ft .  The road bed is 20 ft wide, and carries two lanes of traffic.  The bridge's roof is sheathed in asphalt, and its walls are finished in vertical board siding.  Built in 1937, it is the first wooden covered bridge in the northeastern United States to use modern engineering techniques (the Teco truss).

Contoocook River: The Contoocook River ( ) is a 71 mi river in New Hampshire.  It flows from Pool Pond and Contoocook Lake on the Jaffrey/Rindge border to Penacook (just north of Concord), where it empties into the Merrimack River.  It is one of only a few rivers in New Hampshire that flow in a predominantly northward direction.  Two picturesque covered bridges in Hopkinton and one in Henniker span the Contoocook, as does another on the Hancock-Greenfield line.  Residents and tourists have made the Contoocook popular for fishing and whitewater boating.

Contoocook Railroad Bridge: The Contoocook Railroad Bridge is a covered bridge on the former Contoocook Valley (first Concord & Claremont, later Boston & Maine) Railroad line spanning the Contoocook River in the center of the village of Contoocook, New Hampshire, United States.  It is referred to in the National Register of Historic Places as the Hopkinton Railroad Covered Bridge, for the town of Hopkinton, New Hampshire, in which the village of Contoocook is located.

Greenfield, New Hampshire: Greenfield is a town in Hillsborough County, New Hampshire, United States.  The population was 1,749 at the 2010 census.  Greenfield is home to the Crotched Mountain Rehabilitation Center, to Greenfield State Park, and to part of the Wapack Trail.

Contoocook River Amusement Park: Contoocook River Amusement Park was a trolley park in Penacook, New Hampshire.  The park was developed along the south bank of the Contoocook River.  For twenty cents in 1893, and up until the 1920s, one could ride 7 mi on the trolley from downtown Concord to Penacook to enjoy free entertainment, fireworks, swimming, dancing at a large pavilion, boating, roller-skating, bowling, and even a steamboat ride up the Contoocook River.  The park closed in 1925.

Contoocook River Railroad: The Contoocook River Railroad, or CRR, is a former railway company in New Hampshire.  The CRR was first established on June 24, 1848, as "Contoocook Valley Railroad" founded and built on a standard gauge railway line from Contoocook to Hillsboro which was opened in December 1849.  The 14.7 mile long route branched in Contoocook with the Concord and Claremont Railroad.  The southern continuation of this path toward Massachusetts was subsequently amended to include the Peterborough and Hillsborough Railroad.

Contoocook Lake: Contoocook Lake ( ) is a 344 acre water body located in Cheshire County in southwestern New Hampshire, United States, in the towns of Jaffrey and Rindge.  The lake, along with Pool Pond, forms the headwaters of the Contoocook River, which flows north to the Merrimack River in Penacook, New Hampshire.

North Branch Contoocook River: The North Branch of the Contoocook River is a 17.9 mi river located in southwestern New Hampshire in the United States.  It is a tributary of the Contoocook River, part of the Merrimack River watershed.

Highland Lake (Stoddard, New Hampshire): Highland Lake is a 697 acre water body located in Sullivan and Cheshire counties in southwestern New Hampshire, United States, in the towns of Washington and Stoddard.  The lake has two outlets.  The north outlet feeds Shedd Brook, while the south outlet flows through Island Pond to the North Branch of the Contoocook River.  Water from the two outlets rejoins in the town of Hillsborough, approximately 8 mi east of Highland Lake and one mile upstream from the Contoocook River.  The northern end of the lake is only accessible by boat through a channel approximately 50 feet wide.

Supporting paragraphs: Contoocook River Greenfield, New Hampshire
Answer: Hillsborough