Drew Barrymore and her fiance Will Kopelman on January 25, 2012 in Washington, DC. Credit: Paul Morigi/WireImage

Drew's bride-to-be bliss!

Engaged and expecting her first child, Drew Barrymore couldn't be more happy to head into summer with her fiance Will Kopelman, 34, by her side.

"She is so thrilled to be expecting," a source tells the new Us Weekly of Barrymore, 37. As she prepares for impending motherhood, the star is also just as hard at work planning her June walk down the aisle.

The new issue of Us Weekly (out Friday) reveals that Barrymore has already crossed off two key to-do's from her list: The venue and her all-important dress!

According to a source, the mom-to-be will don Chanel for her ceremony, to be held at her Montecito, Calif., home.

Barrymore -- who began dating in January 2011 and accepted Kopelman's proposal a year later -- is in full-tilt wedding planning mode.

The actress "is really focused on the wedding right now," says the friend. "She will be even more excited about the baby after that!"