Мне неизвестно, где он живёт.

I do not know where he lives.

Breakdown of Мне неизвестно, где он живёт.

• мне: me
• где: where
• он: he
• жить: to live

Questions & Answers about Мне неизвестно, где он живёт.

Why is it мне, not я?

Because the Russian structure is literally closer to To me, it is unknown where he lives.

• мне is the dative case of я
• Russian often uses impersonal patterns like this to express things such as:
  • Мне холодно = I am cold / literally To me, it is cold
  • Мне интересно = I am interested / literally To me, it is interesting
  • Мне неизвестно = It is unknown to me

So мне is not the subject. It marks the person to whom the state applies.

What exactly is неизвестно here?

Here неизвестно functions as a predicative word: something like unknown or not known in an impersonal sentence.

A useful way to understand it is:

• известный = known, famous
• неизвестный = unknown
• неизвестно = it is unknown / unknown

In this sentence, неизвестно does not agree with a noun. It works as the main predicate of the whole clause:

• Мне неизвестно = It is unknown to me

So this is not the same as using a normal adjective before a noun, like:

• неизвестный человек = an unknown person

Why is неизвестно written as one word, not не известно?