Maps are essential for genealogical research. While current maps are interesting, particularly if you are traveling to where you ancestors lived, the older maps are valuable also. Fortunately there are many map collections on Internet and they continue to grow as there is a demand for them.
Some of my favorite Internet map sites include the U.S. Genealogy Map Project: State, County, Territory Maps http://usgenmap.rootsweb.ancestry.com/usgenmap.htm. In this collection there are U.S. Border/Land Claims Maps for 1783-1959 in various categories. A new feature on the web site is "County Name to State Cross Reference." You will be able to determine which state or states in which a particular county is located. The maps show the formation of territories and states by years, plus a chronology of the acquisition of the land.
An extensive set of maps can be found at Historical County Lines http://www.his.jrshelby.com/hcl/. You can link to the Newberry Library web site of Historical County Boundaries; Family History 101 maps; American Indian Territorial Losses from Map.com; University of Texas (Austin) US Territorial Expansion maps; University of Connecticut Library US maps (1834); Color Landform Atlas of the United States; AniMap with SiteFinder Online and Global Gazetteer of the American Revolution. A shortcut to each state is at the top of the Historical County Lines home page. Select a county and you will link into a variety of maps available on Internet for that particular state.
County Boundary Map http://maps.huge.info/county.htm is a interactive web site that allows you to enter a zip code and find the county. Another way to search is to click on a state from opening the US map and keep clicking until you locate the county you wish to find. Neighboring counties will be found when you keep clicking off to the side of your selected county.
A valuable collection of state maps and information can be found at the U.S. Census Bureau http://www2.census.gov/geo/maps/general_ref/cousub_outline/cen2k_pgsz/.
The web page contains links by state to pdf files. There is a current map on the first page of the file followed by a county subdivision outline map plus information on locations. Each subdivision has a map showing the counties and communities. In the case of counties which have townships, this information is very valuable when doing genealogical research.
If you are researching in the United Kingdom, be sure to check out old-maps.co.uk Counties Gazetteer.
Be sure to check out the County Gazetteer on the same web page. Locate a place, click and you will find the map that coordinates with it. Excellent maps of Scotland can be found at the National Library of Scotland web page http://maps.nls.uk/. Some of the county maps date back to the late 1500s. Colorful maps of England, Wales and Scotland, linking to maps of various time periods can be found at Genmaps http://freepages.genealogy.rootsweb.ancestry.com/~genmaps/.
Click and have some fun. You can save some of the maps to your hard drive to search and include in your ancestry.