Guilielm, Guillaume, Gullam, Gwilliam, Gwilym, Wilson, Willimon, Williman, Williamson, Whilly, Whillie
From the German name Wilhelm, a combination of the words "will" and "helmet", brought by the Normans. The Welsh adopted it as Guilielm and Gwilym, becoming Gwilliam and Gullam. Thought to be the 2nd most popular surname in Wales. In use worldwide through migration from Wales, predominant in Wales in Caernarfonshire and Ynys Mon, its a popular name all over Wales and the English speaking world today through Welsh migration.
Williams is the second most popular surname in New Zealand and possibly the 3rd most popluar surname in the USA! You are a big family indeed!