A source close to the newlyweds tells us friends and family were invited to the couple's home Saturday for the wedding -- we're told it took place in the backyard -- and was extremely intimate.

Hilary later shared a photo of her and Matthew decked out head-to-toe in their wedding gear. You can tell they went with a simple approach, with huge smiles and an old-school whip parked just behind them.

Hilary and Matt got engaged back in May after dating for several years. Duff gave birth to the couple's daughter, Banks, in October of last year. She has a 7-year-old son, Luca, with her ex-husband, Mike Comrie.

Hilary has a busy year ahead ... it was recently announced that as part of its new programming, Disney+ will be doing a reboot of "Lizzie McGuire" which she starred in from 2001-2004.