From its beginnings in 1886 until its gradual decline following World War II, nearly thirty Icelandic Unitarian congregations were organized in Western Canada, the Upper Midwest and Washington state. At its peak in the 1930s, there were eighteen active churches and preaching stations.
via Icelandic Unitarians.
The influence Unitarians had in Iceland and the number of Icelanders in North America that became Unitarians is not well known. Here is an attempt to give some overview.