You are right. Mount Ranier is #24.http://americasroof.com/fourteeners.shtml
But at http://en.wikipedia.org/wiki/Mountain_peaks_of_the_United_States is says Mount Ranier is #17!
Your source is using the different summits on the same mountains. Example: it is counting both summits of Mount McKinley as two separate peaks. My source (Yes, I know it is Wikipedia, but common sense and numbers don't lie!) just names the highest peak as the height of the mountain.