我有一枚正方形硬币，不知是什么国家的？

荷兰。

不是很值钱，别报太大希望，没有中文资料。
看这个吧
Welcome to the "Estates-Antiques" Ebay auction. This could be your chance to bid on an item that has brought pleasure to someone for many years. Now it is your turn to receive the blessing of owning this wonderful piece. I am delighted that you have chosen to look at my collection. Have a nice day and bid away.

This auction is for a 1915 KONINGRIJK DER NEDERLANDEN ONE CENT PENNY COIN. This is the first time I have ever seen a coin like this. It is very neat and has some very nice detail. That is all I know about this old coin. The detail is very very nice and it is a great looking coin. As you can see in the picture it is a very very pretty coin and will make someone very happy. I hope someone realizes the value of this coin because I am listing it with NO RESERVE! This is one of many coins I have to list. I just bought a huge estate with lots of coins and paper money in it. Have fun bidding on this wonderful estate