Nick Flanagan, who won last week's BMW Charity Pro-Am at The Cliffs and is the Nationwide Tour's leading money winner, posted a 5-under-par 67 and is among a large group tied for fourth place.
Williamson, who won the Fort Smith Classic three weeks ago, began on the back nine Thursday and did not collect his first birdie until the par-4 15th. He added a birdie at the 17th to make the turn at 2-under par.
On his second nine, Williamson tallied back-to-back birdies at two and three. He birdied the final two par-5s, the sixth and eighth, to grab his share of the lead.
'I'm trying to suck up my pride and hang in there,' said Williamson, who hit 13 of 14 fairways on Thursday. '[The Nationwide Tour] is a great opportunity for me to get back to, not where I necessarily feel I belong, but where I want to be. '
Walker certainly did not look like his name would appear atop the leaderboard after a double-bogey at the first. Three birdies in a row from the sixth got him under par for the championship.
He eagled the par-5 11th and finished his round with three birdies in his last four holes.
The 2004 Nationwide Tour Player of the Year is trying to regain the form that gave him that year's money title and a try on the PGA TOUR. Unfortunately, he hurt his neck and only played in nine events in 2005.
Mills, a former Canadian Tour stalwart, also teed off on No. 10 to start his round. He birdied 11 and 12, then parred his next six holes to polish off his opening nine.
Much like Williamson, Mills birdied two, three, six and eight to join the group at minus-6.
Greg Chalmers, Matt Hansen, Marc Turnesa, Jason Caron, Sal Spallone, Scott Dunlap and former six-time winner on the PGA TOUR and two-time Ryder Cupper, Steve Pate, joined Flanagan at minus-5.