is a 10.6 mile
long (17.0 km
located in southern New Hampshire
in the United States
. It is a tributary
of the Souhegan River
, which flows to the Merrimack River
and ultimately to the Gulf of Maine
Stony Brook rises in the town of Greenfield, New Hampshire, on the northern slopes of North Pack Monadnock Mountain. It flows southeast through the town of Lyndeborough, reaching the Souhegan in the mill town of Wilton.
It is paralleled for most of its length by New Hampshire Route 31 and by the former Hillsboro Branch of the Boston and Maine Railroad.