This is going to seem a really dumb question to anyone from the USA, but I would love to know why one of the above states is pronounced as it's spelt, while the other, though spelled in a similar way is pronounced Arkinsaw.
Can anyone help this poor confused Aussie please ?

Not exactly sure, I am still trying to figure out why the more well known Kansas City, is actually across the river in Missouri.

I remember being suprised and thinking someone was kidding with when I first saw Arkansas spelled rather then spoken.

Well, then there is 'Illinois.' Sounds nothing like it's spelled. More, I'm sure...

Sorry, not "nothing" but singular, never plural...

It is somewhat of an unrelated coincidence that Kansas and Arkansas are spelled similarly. The names have separate origins.

Kansas was named for the Kansa tribe. The plural would have been Kansas.

Arkansas was named for an Algonquin tribe who lived "downstream"--the Ugakhpah. That later became the similar-sounding Arkansas.

Thanks Gary. It has confused me since I was about 11, and encountered Arkansas in a news article I was reading.
Have never found anyone who could explain it before.

This thread has been interesting. I've been to all the places mentioned here: Arkansas, Kansas, and Kansas City (both Kansas's and Missouri's).

The Missouri River flows into the Mississippi River, but those states don't even touch, however, they do get close.

Illinois is a French word which is why the 's' is not pronounced. As for the pronounciation of Arkansas, the state government had it changed from 'Ar-Kansas to Arkansaw' so as not to be confused with Kansas.
Also in the state of Kansas, they pronounce Arkansas as it is spelled.

If Illinois were pronounced as a French word, though, wouldn't it be Ill-en-wah (more or less), rather than Illinoy?

I think the thing with Illinois is that pronunciations like this always end up very different over time, e.g. I've heard Boise, Idaho, pronounced like "boys" - I'm unsure if that's how most people would pronounce it or not, but I'd say "bwahz", as it's named for the French word. Or Des Moines, Iowa - I'd say "day mwahn" but have heard "dess moyns". Another example may be Germanic surnames such as Weinstein, which would in Germany be pronounced as "v-eye-n-sht-eye-n" (hope this is clear, I'm not sure how else to convey the "eye" sound), but from Americans you nearly always hear "wine-steen".

All I know about Boise is that Harry Chapin mentioned it in "W*O*L*D", and he called it Boyzee.

Ah, well, perhaps "boyzee" is the more common American pronunciation? A friend of mine from Pennsylvania also pronounces it like that!