This is a followup to my previous post.
I found a record online for a Joannes Petrus Ohlert who was born in the Catholic parish at Mutscheid, Rheinland, Prussia on 9 Dec 1822. The name and birthdate are a potential match for the John Peter Ohlert who was living in the Grimm household with Gertrude and Joseph in Peru Township, Iowa, and then later in Minnesota.
I looked up Mutscheid on google maps, and it turns out that the neighboring town is called Schönau. That is a match to the name of the parish on Joseph's birth certificate. The town of Schönau is now technically part of the city of Bad Münstereifel.
Then I found that there is a farm 2 kilometers north of Schönau called Lingscheiderhof. Hmmm. That name looks familiar. So I looked up the name of the church in Schönau (St. Goar) and sent an email.
Yesterday I received an answer from the church. Indeed the name of the pastor in 1855 was Johann Hübbers. This was the person who signed Joseph's birth certificate. He was the pastor from 1834 - 1860. According to the church, Antonius Lingscheid and Gertrudis Hündgen were married 24 Jan 1845 in the town-hall of Münstereifel. Under regulations in effect at the time, they had to marry at the town hall before they could marry in the church. They were married in the church on 25 Jan 1845. The entry in the church book states that they were both from the hamlet of Bouderath, which is just outside Schönau. The church also confirmed that Johann Peter Ohlert and Gertrud Hündgen were married on 15 April 1852.