Where does Drow live?

You'll find Drow in Underground according to the bestiary entry.

Drow

· · CR Unknown

Ranges across underground; Drow lists at CR 1/4 as a medium humanoid (neutral evil). AC 15, 3 hit dice, 30-ft speed. Senses include darkvision 120 ft. Speaks elvish and undercommon. Notable trait: Fey Ancestry — The drow has advantage on saving throws against being charmed, and magic can't put the drow to sleep.. Sourced from Monster Manual (5e 2014).

Stat Block

Challenge Rating: Unknown
Type: —
Size: —
Alignment: —
Speed: —
Habitats: Underground
Sources: Monster Manual (5e 2014)

Ecology

Drow are subterranean elves of the Underdark, organized into matriarchal city-states that worship a goddess of spiders and treachery. Society is rigidly stratified by house, with noble families ruling over commoner clans, slave castes, and alliances of mercenaries. Patrols, scouts, and traders are sent to the surface and to neighboring Underdark settlements; these encounters with the wider world produce most non-drow contact. Most drow live their entire lives within their natal city.

Behaviour

Drow are paranoid, intricate, and patient. The political culture rewards betrayal at the right moment and punishes it at the wrong one, producing individuals who think three moves ahead and trust no one fully. They are not uniformly cruel; many drow privately disagree with their society's worst practices but keep silent because dissent is fatal. In contact with surface peoples they are cautious, suspicious, and quick to assume hostility — usually correctly.

Origin

The drow descend from elves who fled or were driven into the Underdark following an ancient civil war between elven factions. The defeated faction made compacts with the spider-goddess to survive, and the price of those compacts shaped every aspect of subsequent drow culture. Some drow lineages remember the old surface origins; others reject the history entirely and consider the Underdark their only homeland.

Underground