Ajaccio
Alençon
Antibes
Avignon
Béziers
Bourges
Cambrai
Castres
Créteil
Le Havre
Lorient
Quimper
Roubaix
Valence
Le Havre
A word that has seven letters is unknown, in French: 'inconnu'.
Belfast is the only city in Ireland with seven letters in its name. Many, many towns and villages have seven letters in their name, but no other city does.
Marseille.
Paris
Orlando
Some countries of seven letters where French is an official language would be Belgium, Senegal, Burundi, Comoros & Vanuatu.
They type of French castle that begins with the letters ch and has seven letters is a chateau. A chateau can be with or without fortifications and is usually where someone of nobility resides.
see links vv
"agreste" and many others
Agen is a city in France. Agde is a village in France.
Paris, Dijon, Lille, Reims and Rouen are the ones I can think of.