Prior to his retirement, Sir Alex Ferguson agreed to send a side north after discussions with County director of football George Adams, who was part of the coaching staff with Ferguson at Aberdeen.
The match is scheduled for Saturday, 20 July, a fortnight before the Highland club open their SPL campaign at Celtic.
County chairman Roy MacGregor said: "Thanks to an agreement between George and Sir Alex, the game will go ahead next month.
"We are delighted about this and cannot wait for a Manchester United select, which could include a few first-team players, to fly up for this match.
"With the new pitch being laid this month, we didn't really want to play a match here before the start of the season, but clearly this was too much to resist. To have Manchester United be our opponents - to christen the pitch - is terrific news.
"The last time they were here, I believe, was in the 1970s, so it's fitting they are coming back now for an occasion when our new stand will be complete and pitch in place."
United's previous visit to Dingwall for a pre-season friendly was in 1976 - when Martin Buchan and Gordon McQueen were included in a side managed by Tommy Docherty.