A town called Panna Maria (which means "Virgin Mary" in Polish) in south-central Texas is arguably the oldest Polish community in the United States, and certainly the first permanent Polish settlement in the US. The town is sometimes described as "Polonia's Plymouth Rock." There were definitely Polish settlers earlier, but this was the first unified area of established Polish culture in America. Panna Maria also had the oldest Polish school in the US, St. Joseph's school, which now houses a historical museum. This town was settled in the mid-19th century by settlers who were mostly from Upper Silesia. These Polish Texans integrated themselves into frontier life, but the life they lived was not without hardship. Some of the Polish immigrants also settled nearby and founded the communities of Cestohowa and Kosciusko (note the spelling differences from the Polish spellings of "Częstochowa" [named after the city in Poland on the Warta River] and "Kościuszko" [named after Tadeusz Kościuszko, a veteran of both the Polish-Russian War of 1792 and the American Revolutionary War.])
Many Polish people in this area were sympathizers with the Union Army when the Civil War started, so the community received a lot of harassment from people in the area (in addition to the general harassment that arose from xenophobia towards foreigners). Still, there were some who joined the Confederate forces; a good number of those may have been coerced into doing so.
There is a good comprehensive history of the town and the settlers at this link, and continuing here. There is also an excellent website talking about Silesian Texans.
In the 1970s, a uranium recovery plant was built in the area. It was decommissioned a few years later, but the area still suffers from environmental problems as a result.
Over time the Polish spoken in this area became isolated and developed its own dialect with a mix of archaic Polish phrasing, "Pol-Tex" words, and neologisms.
I have been to Panna Maria, which is in Karnes County, about 50 miles southwest of San Antonio. There don't seem to be a lot of people who speak Polish as a primary means of communication any more, as most of the emigration there from Poland occurred over a century and a half ago. It is a small, simple community that appears to not have a lot of wealth. I hesitate to say that it an impoverished area, because much richness can come from within even if there is not a lot of material wealth. It is also a stop on the Texas Independence Trail.