September 8th. Happy Birthday Mary! and Happy Thanksgiving!
On December 8, we celebrate the feast of the Immaculate Conception of Mary. Therefore, it is only fitting that, nine months later, September 8, we celebrate the Nativity of Mary. This feast is less known than that of the Immaculate Conception, probably due to the fact that it is not a Holy Day of Obligation. Nevertheless, it is an important feast that is worth celebrating.
Interestingly, this day is also the day that the First Mass was celebrated on U.S. soil. Only, at that time, the United States did not exist. On September 8, 1565, when the Catholic Spanish explorers landed in Florida, they built an altar and offered a Mass in thanksgiving. This was only fitting, as the Greek word for Eucharist, "Eucharistesas", literally means "gave thanks".
While Florida was not one of the original 13 colonies, there is plenty of reason to celebrate September 8, rather than the fourth Thursday of November, as the first Thanksgiving in United States history. The commonly celebrated Plymouth Thanksgiving feast is by no means the first of its kind. United States federal holidays are based on non-catholic secular calendar. So celebrate the real Thanksgiving holyday. Attend a Mass, and have a large feast in Our Lady's honor!