1850-1885 Index Mortality Schedules. Ancestry offers access to the index for free, but to see the actual image requires a subscription

1888-1895 Special Census. Ancestry offers access to the index for free, but to see the actual image requires a subscription

Marion Co formed in 1832 First Census was 1840
1840 Census Index - Names only
1840 Census Index - page numbers & Township
1840 Census Index - Outside link with page and line numbers
1840 Census - Blythe, Buffalo Fork, Little North Fork & Sugarload townships
1840 Census - Union & White River Townships
1840 scanned images - free from FamilySearch.

1850 Federal Census
1850 Census Families 1-100 - Pages 309A-316A
1850 Census Families 101-200 - Pages 316A-323B
1850 Census Families 201-300 - Pages 323B-330B
1850 Census Families 301-363 - Pages 330B-334B
1850 Census Index - A & B page designations do not match the above. Use the page number only to find family in the above transcriptions
1850 Census - Compare this abstract to the transcriptions above.
1850 scanned images - free from FamilySearch.
1850 Slave Census - Transcription
1850 Slave scanned images - free from FamilySearch.

1860 Census (I can't find any free images for 1860)
1860 Census Index - by head of household
1860 Census Index - Jimmies Creek Township
1860 scanned images - free from FamilySearch.
1860 Slave Census

1870 Federal Census
1870 Census Index - Jimmies Creek Township
1870 scanned images - free from FamilySearch.

1880 Federal Census
NOTE: Terrible spelling & writing - see each page
1880 Census - Jimmy Creek Township
1880 Census - Little North Fork Township
1880 Census - Franklin Township
1880 Census - Sugar Loaf Township & Village of Doddsville
1880 Census - Town of Yellville
1880 Census - Union Township
1880 Census - White River Township
1880 Census - Blythe Township
1880 Census - Bearden Township
1880 Census - Buffalo Township
1880 Census - Water Creek Township
1880 Census - Tomahawk Township
1880 Census - Hampton Township
1880 Census - Prairie Township
1880 scanned images - free at Ancestry.com in conjunction with LDS FamilySearch.
1880 scanned images - free from FamilySearch.

1890 Federal Census
What Happened to the 1890 Census?

1900 Federal Census
Big Creek Township
Buffalo Township
DeSoto Township
White River Township
1900 scanned images - free from FamilySearch.

1910 Federal Census
1910 scanned images - free from FamilySearch.

1920 Federal Census
1920 scanned images - free from FamilySearch.

1930 Federal Census
1930 scanned images - free from the Allen County Library. Use ancestry.com's free search to find your family in the census.
1930 scanned images - free from FamilySearch.

1940 Federal Census
1940 scanned images - free from Ancestry.com in conjunction with National Archives.
1940 Enumeration District Maps and descriptions. Free at Ancestry.com.
1940 scanned images - free from FamilySearch.

Helpful Census Links
Site for Census Tools
       35 free electronic spreadsheets for archiving federal, state and international census data! The U.S. Federal Census spreadsheet has separate pages for each census year from 1790-1930, including the 1880-1920 Soundex. Each page is formatted to faithfully match the actual census for each year. It's a great way to finally organize your census records of an entire family for up to 140 years!