Polonia is an unincorporated census-designated place in the town of Sharon, Portage County, Wisconsin, United States.

In 1858, five Polish immigrant families joined a German farming community at Ellis, two miles to the west of what would become Polonia.

[4] Some of the newly-arrived Poles at Ellis worshiped there with their German neighbors at St Martin's Catholic church for a few years, but after their numbers swelled to twenty or thirty families,[4] they split in 1865 into a separate Polish-speaking Catholic church at Ellis.

Three saloons stood nearby and worship was interrupted too often by noise and brawls at Ellis's saloons, so in 1871 the Polish Catholic church building was moved to a hill two miles to the east.

[5] In 1874 a church school was started at Polonia, staffed by five Felician Sisters who were sent as missionaries from Kraków, Poland.