The pregnant actress, 35, smiled away as she wandered along wearing a long-sleeved black jersey dress that hugged her growing baby bump and paired it with black sunglasses.
Plemons also looked relaxed in a green button-down shirt and gray pants along with a blue baseball cap and dark sunglasses to protect against the bright California sun.
News of their engagement surfaced in January when Dunst was spotted with what appeared to be an engagement ring at the Golden Globe Awards. A few weeks later, the happy couple hit the Independent Spirit Awards together where Plemons, 29, was nominated for his role in Other People.
The couple is now expecting their first child together.
Dunst confirmed her pregnancy in an ad campaign for Rodarte, wearing a white and salmon-colored lace V-neck dress and an array of flowers. She posed with her hands under her baby bump and wore a slight smile.
In an interview with PEOPLE in June, Dunst said she is “very happy” with her former Fargo costar, although she is “not in any rush” to plan their wedding.
“I’m very relaxed when it comes to those kinds of things,” Dunst said, adding, “I’m going to get married at some point!”
While she said she wasn’t in a hurry, Dunst did say she was having fun brainstorming ideas for their nuptials — and using a very popular website to do so!
“I never thought I was that person who’d have a Pinterest board. I like doing all of that pinning things,” Dunst told Kelly Ripa and Ryan Seacrest in September on Live with Kelly & Ryan. “It’s really fun, and because we create it together from the beginning, it’s a really nice thing to do together. It’s going to be so personal and fun. We’re having a really good time.”