I'm a native speaker and I have never ever heard anyone say Indian file before. Generally, using ethnicity in descriptive terms is pretty uncommon these days as language changes to become more socially and racially inclusive. I would avoid it 😊

'Single file' is commonly used. Like Amy, I've never ever heard 'Indian file'. Google tells me it's an American term originating in the 18th century. I'm sure it's no longer used and, as Amy says, would be considered offensive. (Native Americans are no longer referred to as Indians.)

Indian file is a very old way of saying one behind the other. It is a reference to how that the Native Americans would move in the forests, supposedly to make it difficult to determine how many there were. I don’t think it is offensive, as I can’t see it is a negative assumption of a race, but we live in more sensitive times. Some might find the term ‘Indian’ to inaccurate and offensive. I am not sure how accurate it is, bearing in mind in thick forest, how else would you move?

I am a Canadian and I grew up very close to the Canada - United States border. I have heard both expressions used. But, in Canada, single file was used at school. I watched American television and did hear Indian file on occasion. I haven't heard the term in over 60 years now, since the late 1950's. I agree with Amy and Claire. The term Indian file is antiquated and would be considered offensive now.

*Considered