Philly. Enough said.
Not just Philly. There are numerous former churches in PA (and other states, but I live in PA so these are more familiar to me) -- which have been purchased by muslims and now operate as mosques and madrasahs (schools). They are in rural, deep red communities as well as cities. They arrive suddenly in towns where there was no previous muslim presence. Realtors can help you locate religious buildings for sale in the past few years, and find the names of the new owners. It's an eye opener.
I call this phenomenon Jihadi Appleseed.