The problem in the US is that time zone boundaries very frequently do not match state boundaries.

It’s common for major cities to be located on rivers that are state boundaries, the area around the city uses the same timezone, and one of the states has a timezone boundary in the middle. Indiana has many tz database entries because of this kind of thing.

There are other fun cases like the Navajo Nation in Arizona.

14 states have more than one time zone[0].

I live in South Dakota, which is one of them—the Mountain/Central timezone boundary within the state follows the Missouri river. (Locals refer to "East River" and "West River" to refer to the two halves of the state. The capital, Pierre, is technically East River, but is right on the banks, almost dead-center.)

[0]: https://simple.wikipedia.org/wiki/List_of_U.S._states_and_te...