Are your members mostly Unitarians by birth, or does First Unitarian attract lots of unchurched people and ex-(Catholics, Baptists, Uniteds, Anglicans, Lutherans, Jews, etc., etc.)?
As with North American Unitarian Universalists in general, the vast majority of us at First Unitarian have arrived at Unitarianism from either another faith tradition or from no faith tradition at all. Our congregation is home to a wide variety of ex-(fill in the blank)s as well as to the previously unchurched.