The the two women were pictured dipping their feet in the sea.
Mrs Johnson wore a red mid-length dress, which appeared to be a £325 gown by London-based designer L.K.Bennett, for the walk.
Dr Biden wore a black and white polka-dot dress with a black blazer.
The First Lady’s blazer, which carried the word “love” on the back in studs, appeared to be by French brand Zadig and Voltaire.
After having tea with Mrs Johnson this afternoon, Dr Biden told reporters: “It’s really nice to be here in Cornwall. It’s my first time.
“Obviously it’s beautiful for those of you who have been here before.”
She said that she and her husband were looking forward to meeting the Queen as part of their visit.
Dr Biden added that the couple hoped to focus on education in their discussions with the royals.
She said: “We’ve looked forward to this for weeks and now it’s finally here. It’s a beautiful beginning.”
More to follow…