Unitarians (and Universalists) were Christian many years ago, with Unitarianism being a Christian rejection of the Trinity and Original Sin. The Unitarian "Godfather" Michael Servetus was a Christian burned at the stake by Calvin in the 1500s due to his anti-Trinity and anti-Original Sin writings.

However, over the years, Unitarian Universalism (a combining of the denominations in 1961) has become an interfaith/multi-faith church that includes Christians, Jews, Hindus, atheists, agnostics, etc. There are a few Christian Unitarian congregations in the United States, but most are multi-faith.

There are Unitarian churches in England and Romania, and they are still Christian.