The state highway department puts out a free road map that will suffice if you stick to paved roads. Request a copy from Travel Montana, the official Montana travel information source (301 S. Park Ave., Helena [1], MT 59520-0533, 406/841-2870 or 800/847-4868, www.visitmt.com [2]).
For a more detailed look, the Montana Atlas and Gazetteer is a handy book of topographic maps covering the entire state. It’s $19.95 and is available at most bookstores in Montana or from De Lorme Mapping (P.O. Box 298, Freeport, ME 04032, 207/865-4171).
National forest maps are invaluable for off-the-beaten-path travel in the western part of the state. Day hikers sticking to established trails will usually be able to navigate nicely with these maps, available at local ranger stations or from the U.S. Forest Service Northern Region Headquarters (P.O. Box 7669, Missoula [3], MT 59807, 406/329-3511); they’re $5.95 from the government, a bit more if you buy them from a bookstore.
Serious backpackers and hunters will want U.S. Geological Survey quadrangle maps. Many sporting-goods stores carry these maps for the more popular areas; they can also be ordered directly from the USGS, Federal Center (P.O. Box 25286, Denver, CO 80225, 303/236-7477). It pays to do a little library research before contacting the USGS; they’ll want to know the exact names of the maps you’re ordering.
Links:
[1] http://www.moon.com/destinations/montana/butte-helena-and-southwestern-montana/helena
[2] http://www.visitmt.com
[3] http://www.moon.com/destinations/montana/missoula-and-northwestern-montana/missoula