From vs. Than

[Studentlearner]

I was taught that it is different from. I can’t remember why that is. I hear a whole lot of people say, “different than”. Which one is correct and why?

[Tdol]

You'll hear different from/to/than, so I'd say they're all correct.

[MikeNewYork]

I was taught that it is different from. I can’t remember why that is. I hear a whole lot of people say, “different than”. Which one is correct and why?

In AmE, "different from" and "different than" are the more common.
In BrE, "different from" and "different to" are the more common.

Different from works best for either variant.

[Tdol]

But we almost always use use 'differ from'- is that the same in the US?

[MikeNewYork]

But we almost always use use 'differ from'- is that the same in the US?

Yes, same here. The other two appear to come from comparisons in other expressions:

compared to
[verb] differently than