Does anybody know from how far away you can see Mt. Rainier?

I lived in Western Washington for over 30 years.

On a clear day, from a high point with a clear line of sight, you can see the Mountain from at least 150 miles away, in some cases from even farther.

I have pictures of the mountain that I took on campus at my college in Seattle which is a straight-line distance of about 60 miles. The mountain is still huge and the dominant feature in the picture so if you just want to be able to "see" the mountain you could be much further away - again assuming you have a clear line of sight and clear weather.

I also have a picture that was taken from an aircraft on a vacation a few years ago looking south at Mt. Rainier. You can see Mt. Adams, Mt. St. Helens and Mt. Hood in the background. Mount Hood is in Oregon about 150 miles away and is much smaller than Mount Rainier. The picture was taken with a cell phone with no zoom.

So yeah, in the right conditions you can see Mt. Rainier from at least 150 miles away, potentially farther.

Wikipedia says that in the right weather conditions and from the right point of view it can be seen as far south as Corvallis and as far north as Victoria BC.