There are three archival repositories on the U of I campus:

Special Collections & Archives in the Main Library

The John Martin Rare Book Room at the Hardin Library for Health Sciences

The Canter Rare Book Room at the Rita Benton Music Library

Each of them is home to non-circulating collections of archives, manuscripts and more, and each collection is searchable via InfoHawk+

Special Collections & Archives and the John Martin Rare Book Room each have reading rooms accessible to the public, where you can view their holdings (though the John Martin Rare Book Room is currently under renovation--please contact Damien Ihrig for more information) 

The Iowa Digital Library is home to digitized versions of items from some of these collections.