The historic hotels listed above are all fairly recent additions to the Westin chain, aside from the St Francis, which is the longest current member of the chain, having joined in 1954.

These other hotels are also over 50 years old, like the Continental Plaza/Westin Michigan Avenue, and have been part of Western International/Westin the entire time:

- Bayshore Inn / The Westin Bayshore - 1961
- Calgary Inn / The Westin Calgary - 1964
- Washington Plaza / The Westin Seattle - 1969
- Crown Center Hotel / The Westin Crown Center - 1970
- Houston Oaks Hotel / The Westin Oaks, Houston - 1971
- South Coast Plaza / The Westin South Coast Plaza - 1971
- Edmonton Plaza / The Westin Edmonton - 1972

Although they're all technically over 50 years old, they've all been gutted and renovated numerous times, and none of them have any particular charm. I don't think anyone would classify them as historic.

BTW, Western International Hotels properties didn't carry the chain name, they all had individual names. That changed when the chain became Westin in 1981. Within a few years, pretty much all the hotels in every city were renamed simply The Westin. This was obviously hugely confusing, so they started getting geographically specific names later in the 80s/90s, like The Westin Michigan Avenue.