Jefferson did say he wished everyone in America would become a Unitarian. But then Unitarians never had a creed everyone had to follow so he wasn't really imposing anything on anyone.
Oddly enough, at around the same time Jefferson made that statement, Unitarians and Congregationalists were engaged in a fight with Universalists and Baptists in Massachusetts who wanted to insert a clause into the state constitution mandating separation of church and state. The latter two resented state taxes going to fund Unitarian and Congregationalist churches. They lost the battle. Taxes were levied to support religion for another 15 years or so.
Q: What's the difference between a Universalist and a Unitarian?
A: Universalists believe God is too good for there to be a Hell. Unitarians believe they're too good for there to be a Hell.