Counter for islands?

Question

I have found the following sentence in my practising book (only 日本 is written in kanji because it's in one of the first lessons):

日本は しまが ６８５２ とう あります。

1. I am guessing that とう is the counter for islands. Is that right?
2. Can it be written 島 like しま?

Answer 1

You are correct on both accounts. With the kanji for 島 being used, this sentence would be written as

日本は島が６８５２島あります。

The first 島 would use the kun reading しま and the second would use the on reading とう.

Source: http://www.benricho.org/kazu/shi.html