It's worth noting that:
* Many actresses have played Glinda over the years, both on Broadway and in various touring productions.
* Some actresses have had longer stints in the role than others, but keeping track of individual runs across multiple productions is difficult.
* The "longest run" could be interpreted in various ways (initial run, longest consecutive run, total time spent in the role, etc.).
Therefore, while Chenoweth's initial run is the longest on Broadway, it's hard to definitively say who has played Glinda for the *longest* overall.