In Polk County they accept cash, check, or money order; made out to Julie M. Haggerty, Polk County Recorder. (I wouldn't send cash in the mail). Both of you & your witness have to sign the application in front of a notary & then s/he notarizes it. Mail it back to Polk County Recorder, 111 Court Avenue, Rm 245, Des Moines IA 50309-2251 The time of snail mail typically eats up the three day waiting period. The license is good for six months after the date signed so you have plenty of time to use it.
 
Marriage license applications can be downloaded at Application
 
Although the link for the Application is Story County it can be used for any county. Just fill in the appropriate county on the top right of the form.
 
 If you are getting Married in Des Moines I recommend you mail it to Polk County instead of Story County so it is available in Des Moines when you want to pick it up. The fee statewide is $35 and can be check, cash or money order (no credit cards).
 
Here is the link for Polk County Recorder for more info
 Polk County