It's not exactly impressive that no US state had a practicing Jew as its governor until 1915 when previously-profiled Moses Alexander took over Idaho. The key word here is "practicing".
The first person of Jewish descent to become a governor was David Emanuel, who ran Georgia for eight months in 1801. Emanuel converted to Christianity, so we really can't count him.
It took until 1870 for another Jew to become governor, when Edward Solomon took over the Washington territory. That's right, Washington wasn't a state back then, so we can't really count him.
Which gets us to 1887, when Washington Bartlett, the former mayor of San Francisco, became Governor of California. He died in office after nine months. So, if we ignore the word "practicing", Bartlett was the first Jew to become a governor of a US state.
Why are we devoting a full profile to such an inconsequential figure? Let's just say that while he might just be a footnote in American Jewish history, Washington Bartlett was quite, what's the word... impressive.