Where is the ozone layer?

The ozone layer is located near the bottom of the stratosphere.

The ozone layer is a region with a relatively high concentration of ozone, and is located near the bottom of the stratosphere. It is located 8 to 50km above sea level. The altitude varies with latitude, placing the stratosphere and the ozone layer closer to the Earth's surface over the poles.

The highest concentration is in the lower stratosphere, also called the tropopause. Ozone is found in some concentration in all layers of the atmosphere. Ozone in the troposphere (near Earth's surface) is one component of smog.

Ozone concentrations vary from near zero at extreme elevations (high in the exosphere), to a maximum (~9 ppm) at the bottom of the stratosphere, to zero again near Earth's surface. Some ozone is found in every layer of the atmosphere (usually less than 1 ppm, except for the stratosphere).

(for more information, see the related question)
The ozone layer is in the upper atmosphere of the earth.