Most of Middle East and North Africa from 7th century on. Most of the area of current Spain and Portugal was under Islam rule for 5 centuries.
Currently? Sweden's Malmö is probably the closest example of a slowly happening "takeover".
https://en.wikipedia.org/wiki/List_of_cities_in_the_European_Union_by_Muslim_population
Is this a problem? That I don't claim to definitely know, but it doesn't feel like a great direction for a secular atheist such as myself.