Under Indiana law, counties were required beginning in 1818 to keep a record of their marriages (with some keeping records even before then). Hendricks County was officially formed in 1824, so its marriage records exist from 1824 onward.
Plainfield library has a collection of marriage licenses, which were found in the Hendricks County courthouse. The Indiana Room section of their website has an index in progress (pictured).
Hendricks County GenWeb site. NOTE: There are some flaws in the WPA marriage index - it does not include any entries from Book 1 1/2 (which covered 1831-1837), and errors have been found in the names and book and page numbers.
The WPA also did an index of Hendricks County's marriage supplements books for 1882 through 1920. That WPA marriage supplements index (pictured) consisted of the name of the bride or groom, their father's name, their mother's maiden name, their age as of their next birthday, the date of the marriage, and the corresonding book and page number. The WPA marriage supplements index has been converted into a searchable database, available in the Data section of the Hendricks County GenWeb site.
Hendricks County Clerk's office has Hendricks County's marriage records. They are on the 2nd floor of the Hendricks County courthouse in Danville.
Hendricks County's marriage license books for 1824-1950, marriage affidavits for 1866-1879, marriage supplements for 1885-1906, and marriage applications for May 1905-1947 have been microfilmed. That microfilm is available at the Family History Library and the Indiana State Library. The Plainfield library also has some (but not all) of this microfilm collection - their marriage license books microfilm covers 1824-1925 and their marriage applications microfilm covers May 1905 - January 1922.
The Archives on the Hendricks County Government website includes digital files of the Hendricks County marriage license books for 1824-2003.
Hendricks County GenWeb site has an index to the Hendricks County marriage license books in their Data section. This searchable index (pictured) includes the names of the bride and groom, their date of marriage and the corresponding book and page number. It is an ongoing project--so far it covers 1824-1848 and 1904-1964.