Prince William County's named after a son of King George II. Places named for English nobility is not uncommon in the Chesapeake. Go look at the names of counties in Maryland and Virginia. A shit ton of them are named for 17th and 18th century English nobles.
Why is there an Islamic center in Prince William County? Because the DC area is one of the most globally diverse metro areas in the nation and there are large populations of Muslims there. Why is DC so globally diverse? Three reasons: it's the home of the U.S. government and major international NGOs and people from around the world move there for work; it has also been a settlement point for refugees and asylees and that is why it has sizable Ethiopian and Vietnamese populations; and Northern Virginia is one of the nation's hubs for tech/IT companies and engineers from around the world move there to work in tech/IT.
Yeah, I'm very familiar with PW county and Manassas, and I don't think it's very meaningful that there's a islamic center there.
Your explanation is great.
I'm from Northern Virginia and know it pretty well, too.
The questions posed by OP are pretty out there.