Just adding up all the ages it would seem pretty unlikely that he got married in Holland. If the Windmill was built in 1846 when he got back from Amsterdam he would have been only 20-24 years old. There is a national database called Genlias and they have marriages from 1836-1922 for Amsterdam and there were no hits. Amsterdam is a little problematic compared to the rest of the country, it is not as easy to find records because much hasn't been transcribed. The only census useful is an 1853 one when he was already back in Ireland. Unless he came back with a wife and/or children born in Holland its probably a goose egg. I would check out the familysearch website for original records and see if you can get lucky. Another anvenue is to order microfilm off their website, you can view the microfilm at their family center's. Finding the marriage license of him and Anne Murphy would be helpful, it could yield significant information.