Arnprior is a town in Renfrew County, in the eastern portion of Southern Ontario, Canada. It is located at the confluence of the Madawaska River and the Ottawa River in the Ottawa Valley. Arnprior has experienced significant growth in populations with the widening of the 417 Provincial Highway to four lanes. The Town experienced an increase in population by 13.4% from 2006 to 2011 and the current population is estimated at 9153.