Well, we don't really separate walking and hiking in the Norwegian language (I actually had to google the difference).
According to Statistics Norway[1], 85% of the Norwegian population has taken a walk of 3 hours or less in the last 12 months (of 2014) and around half a walk of more than 3 hours.
I didn't find updated stats about frequency, but in 1998 46% of Norwegians went on walks for longer than 30 minutes at least 2 times a week [2]. I don't have a reason to believe it has changed significantly.