Bad news, men everywhere ... Kristen Bell is officially off the market -- TMZ has learned, she and longtime boyfriend Dax Shepard have finally tied the knot.

The couple had a no-frills ceremony at the Beverly Hills County Clerk Office. We're told there was a photographer present, and Kristen was crying.

According to eyewitnesses, Kristen and Dax went to the clerk office just to get their marriage license -- but when a court employee offered to marry them on the spot, they agreed ... and conducted the ceremony in a nearby courtroom.

Not a huge surprise ... Kristen has talked about wanting a courthouse marriage in the past, saying, "I feel like we get enough attention in our daily lives and we just want something sort of private that involves pen and paper."

Kristen famously re-proposed to Dax after the U.S. Supreme Court struck down the gay marriage ban in June ... kind of a solidarity thing. Mazel tov!