Well, this is as good a point to join the fray as any. :)

Lindon was indeed part of Beleriand. It was the remnant of Ossiriand and Dor Caranthir after the destruction of most of Beleriand.

The confirmed population centers would indeed be the twin cities of Mithlond, but I like many other people believe there were cities at Forlond and Harlond (as the names ending in "-lond" seem to imply something other than just natural harborages).

I'm not so sure the Noldor of Lindon were that much of a minority. Many of the Sindar had been slain in the Wars of Beleriand, and many more had sailed over Sea at the end of the First Age.

Also, many of the Sindar emigrated east sometime during the Second Age, thus further denuding the population of Lindon. It's true that some of the Noldor also passed eastward, but I think the majority of them stayed in Lindon.

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The Lord of the Rings: Findegil's Insider's Guide