What time period did the dinosaur Stegosaurus live in?

The Stegosaurus dates from about 155 - 145 million years ago in the Kimmeridgian and Tithonian age of the Upper Jurassic Period. This was in the Mesozoic Era which was part of the Phanerozoic Eon.

Some estimates suggest that it may have survived until the Berrisian (145-140 Ma) in the early Cretaceous Period although this is not generally recognised by most scientist.

The geological time units are as follows

Phanerozoic Eon (545 Ma - Now)

Mesozoic Era (251 - 65 Ma)

Jurassic Period(199 - 145 Ma) Cretaceaous(145 - 65Ma)

Kimmerridgian age(155 - 150 Ma) & Tithonian age(150 - 145) & Berrisian(145 - 140 Ma)