DES MOINES, Iowa (AP) — Iowa Governor Terry Branstad has entered the political record books as the longest serving governor in American history, dating all the way back to colonial times.

On Monday Dec. 14th, the six-term Republican marked his 7,642nd day of service as governor. That's just shy of 21 years in the office. This means Branstad has moved beyond former New York Governor George Clinton, whose service includes some pre-Constitution time, and is far out in front of any recent or current governor.

Most other long-serving governors topped out at four four-year terms, including former South Dakota Gov. Bill Janklow, former Alabama Gov. George Wallace, former Ohio Gov. Jim Rhoads and former North Carolina Gov. Jim Hunt. All served more than one stint in the office.

Helping Branstad, 69, go longer is that Iowa is a rare state without a term limits law. Also, he has never sought higher office. He took a break in the private sector after serving four terms from 1983 to 1999, but came back to oust an incumbent Democratic governor in 2010.

"The odds of anyone passing him in the 21st Century are next to none," said Eric Ostermeier, a research associate at the University of Minnesota who has compiled a comprehensive list of governors' length of service.