It's not exactly impressive that no US state had a practicing Jew elected 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, and he wasn't elected, so he doesn't count.
In 1862, Edward Solomon became the governor of Wisconsin when his predecessor drowned (but he wasn't elected, and we're not sure he practiced). Eight years later, another Edward Solomon (they were cousins) took over the Washington territory. But since Washington wasn't a state back then, 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 be elected 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.