Custer County was formed in January 1881 from Alturas and Lemhi counties. The area that became Custer County will on the the census for those counties in 1880. Idaho Census Maps, shows county formations
1880 & 1900 census at ISU
1870 & 1880 non-population census
1890 Census Reconstructed
1940 census at searchable index and page images
1940 census page images at National Archives
1940 enumeration district maps - Once there select the "State", and go to "County" and then click on "Get ED Map Images" and you will get the entire county
Census Finder

Homestead Records

Government Land Office records: Patents (homesteads, cash sale and livestock) & maps -
Homestead Records or new GLO site

Marriage Records

BYUI Western States Marriage Index

Death Records

Death Records Index 1911 - 1951 (US GenWeb Archives)
Boise County newspaper death notices (includes many from other counties)
Find A Grave
SS Death Index
VA Gravesite Locator
Virtual Wall, Vietnam Veterans Memorial
Legacy Obituary Finder

Civilian Conservation Corps

Idaho PTV transcript
CCC Legacy

Other Aids & Projects

Cyndi's List
Family Group Sheet Project
Family Search includes 1880 census transcription, extracted marriage records, submitted family sheets, new wiki
GenForum messageboards
Rootsweb Resources:   Idaho
We Relate wiki
Civil War Records

Geography, Geology, Mining and Map Links

Custer County current maps
1895 Atlas
1914 county map
Idaho State University Digital Atlas
Idaho Geological Survey
USGS index of Geographic Names
United States Digital Map Collection
Sherry Horton's History in a Fade (includes mining history)
Idaho Museum of Mining & Geology, 2455 Old Penitentiary Road, Boise, ID 83712
Idaho Department of Lands, Gem Guide
Idaho PTV Ghosttowns
Mining in Idaho, ISU's Digital Atlas

Miscellaneous Links

Custer County on
Census Quick Facts
ITD Historic Markers
Idaho State Historical Society
Idaho Post Offices
Ghost Towns
Salmon-Challis National Forest
Library of Congress