Hailed as the "Cathedral of the Marsh" by one of its pastors, St. Andrew's is a large and impressive Gothic Revival style building that rises majestically out of the flat farm fields that surround it. Located in the unincorporated village of LeRoy, only a few miles from the famed Horicon Marsh, St. Andrew's was the center of religious and social life for generations of ethnic German farmers in the area. Between 1849 and 1901, these ethnic German families would build a large religious complex, including a church, school, rectory, and convent.

In 1899, St. Andrew's congregation chose architect Anton Dohmen, a master architect of religious buildings, to design their new church. Dohmen, who excelled in the design and ornamentation of large churches, gave the congregation a building with all the trappings of the Gothic Revival style: pointed arch openings, buttresses, and towers. On the interior, Dohmen designed a high and impressive vaulted ceiling, including a structural rib vault much like those found in medieval churches.

The ethnic German farmers of LeRoy dug deep into their pockets to pay for the new church and had to complete much of the interior work themselves. It was 1912 before they raised funds for stained glass windows, and 1922 before a professional decoration of the interior could be done. But, like with the church itself, the congregation spared no expense for these details. They hired the noted Emil Frei Art Glass Company of St. Louis to create over 20 stained glass windows. These stained glass windows are works of art with vivid colors and intricate details. The decoration of the interior in 1922 also included works of art, small figural murals and medallions.

Over the years, St. Andrew's congregation has maintained their "cathedral's" historic appearance. Repairs and upgrades to the church have been done in a manner that does not negatively affect historic features. When many Catholic churches removed elaborately decorated altars and statuary, St. Andrew's retained them. While many congregations long for new buildings, St. Andrew's members work to retain the viability of their historic church.