Here is a map of Missouri generated from that web site:
This map shows, by county, the percent of adherents to Catholicism for the year 2000, based on Census data.
Brown: 13% - 52%
Red: 6% - 13%
Orange: 4% - 6 %
Tan: 2% - 4%
Yellow: 0% - 2%
This map shows a remarkable reflection of centuries-old settlement trends. The counties adjacent to the Mississippi and lower Missouri Rivers were explored and settled by Catholic French and Spanish colonials in the 17th and 18th centuries and remain very Catholic to this day. These counties also make up the current Archdiocese of Saint Louis, and is well known for having a Catholic culture, unlike outstate Missouri.
When the United States purchased Louisiana in 1803, the westernmost permanent European settlement in Missouri was La Charrette, located in what is now southeastern Warren County. The Lewis and Clark Expedition journals describe this as a French villiage of five families. Warren County today marks the westernmost part of the Saint Louis area Catholicism north of the Missouri.
Later waves of immigrant Catholics tended to settle in existing Catholic areas, such as Saint Louis. But the first wave of German immigrants were drawn to the lower Missouri River valley, downstream from what is now Jefferson City, a region that resembles the Rhineland, and is very good for growing wine grapes. This region today has the beauty and manner of life that is reminiscent of good Catholic rural living.
Anglo-American settlers of the early 19th century, following the lead of Daniel Boone and his sons, tended to settle on the Missouri River more upstream from Jefferson City. This area was called the "Blue Country", and was one of the centers of large-scale slavery in Missouri (the other being the Southern-culture bootheel). Some Catholic missionary work was done in this area in the early 19th century, but it definitely does not have a Catholic culture today: this and the other outstate dioceses tend to keep a very low profile.
Even though the Ozarks, geographically speaking, extend all the way into Catholic Saint Louis County, the "cultural" Ozarks has very few Catholics and they do not make up a significant percentage of the already small population. Religion here is considered "conservative", but should rather be called "individualistic"; Assemblies of God and other Pentecostal groups are popular, but there are many far-from-the-mainstream groups. The main Catholic populations in the Ozarks were wiped out during the Civil War, which was exceptionally bloody in Missouri; many Catholics fled to Springfield and Saint Louis, but large numbers were lost, such as the settlers of the Irish Wilderness in Oregon County.
Northeastern Missouri had many Catholic settlers from Kentucky, these had good support from the missions.
Missouri outside of the Archdiocese of Saint Louis is still officially mission territory.
