Actually, the US is home to the largest population of Assyrian expatriates, although our immigration policies are resulting in rapid growth of the communities in Europe and Australia. However, it should be noted that in Chicagoland and in California and Detroit, the Assyrian population is massive, and indeed the Catholicos was based in Chicago from 1920 until the repose of Mar Dinkha IV; the current Catholicos, Mar Awa Royel, who I have met in person when he was Bishop of California, moved the Patriarchate back to Iraq. The Ancient Church of the East its Patriarchate in Iraq, or rather returned it there, since the Ancient Church of the East broke away from the Assyrian Church of the East after an Indian bishop discovered, reading the canons of the church, that the hereditary Patriarchy was uncanonical, and shortly thereafter, the last hereditary patriarch, Mar Shimun XXIII, controversially changed the calendar to the Gregorian, so the Ancient Church of the East was initially like the Assyrian equivalent of an Old Calendarist jurisdiction.
In total I think they have about 2 million members in the Assyrian Church of the East and 150,000 in the Ancient Church of the East, and of these, 700,000 speak a dialect of Eastern Neo-Aramaic as their primary vernacular language, making this the largest surviving Aramaic speaking community in the world. Indeed a major difference between the Assyrian Church of the East and the Chaldean Catholic Church is that the Assyrian tribe known as the Qaldanaye (I don’t think I am spelling that correctly) mostly stopped speaking an Aramaic dialect in the vernacular and instead mainly spoke Arabic; this also happened to most, but not all, of the Syriac Orthodox. However, the historically Syriac church with the least amount of Syriac or Aramaic fluency seems to be the Maronite Catholic Church, although their liturgical books retain a mostly West Syriac vocabulary, for example, they have the Husoyeh as a major type of prayer, spelt “Hoosoyo”