Maryland has surprisingly good wild trout habitat, and does a good job of documenting it.  Some of the best habitat is found in the western highlands (Garrett and Allegany Counties) tucked in among Pennsylvania, West Virginia, and Virginia (which you might expect).  However, there's another belt of wild trout in the central highlands, relatively close to Baltimore and the I-95 corridor, which you might find surprising.

Probably the best single source of information about trout habitat is the MD water quality designated use maps, which were just published in 2010.  We've created a series of image overlays so you can work with those maps within Google Earth.  Click on the link in the "MD Resources" menu for a web page that will describe the water quality maps in more detail.  In addition, the Eastern Brook Trout Joint Venture's dataset is a "must use".

The image below was created for the 2006 site, and since we think it's pretty, we've kept it here.

Base Map: NationalAtlas.gov
Fish distribution data: Maryland Biological Stream Survey (MBSS)

Each symbol on the map corresponds to a fish survey in the 1995-2002 MBSS dataset that found trout.  Red = brook trout; Brown = brown trout; Pink = rainbows.

A comprehensive listing of findings from the 1995-97 dataset is found here.