@igb Countries with fewer cities than Los Angeles County include the United Kingdom.

@smellsofbikes I'm sorry for your loss. I know how much you loved her.

@Miikka

Harder than expected. I'm only counting the ones where I know the real name (or at least the popular name).

US:
Whistler's Mother (yes, I know that's not the real name, but it's what everyone calls it); Christina's World (Wyeth); Nighthawks (Hopper); Campbell's Soup Cans (Warhol); The Freedom Of Speech (Rockwell).

Somehow the most famous American painting with "American" in its title escaped me.

France: Raft of the Medusa, The Death of Marat, The Horse Fair, Portrait of Louis XIV, Liberty Leading The People.

NL: Girl With The Pearl Earring, Sunflowers, Starry Night, The Potato Eaters, The Night Watch.

Spain: Las Meninas, Saturn Devouring His Son, Guernica, Portrait of Dora Maar, Persistence of Memory. This was the easiest.

Italy: Mona Lisa, The Creation of Adam, The Annunciation, The Birth of Venus, The Last Supper

I can't think of another country where I could get to five paintings. If you let me include sculptures, I could get the UK, but that would be cheating.