He praised April DeBoer and Jayne Rowse, two Detroit-area nurses who are raising three children with special needs. They filed a lawsuit in 2012 because they're barred from jointly adopting each other's children. Joint adoption is reserved for married heterosexual couples in Michigan.
"In attempting to define this case as a challenge to 'the will of the people,' state defendants lost sight of what this case is truly about: people," the judge said.
DeBoer and Rowse said Friday that they'll get married when the case ends, a process that could take years with appeals.
"We will be getting married — when we know that our marriage is forever binding," DeBoer said.
The 31-page decision was filed in Detroit's federal court when most county offices were closed and couldn't issue licenses.
Dave Murray, a spokesman for Republican Gov. Rick Snyder, said the state has an "obligation" to defend what voters chose a decade ago.
If a "court concludes the provision of the Michigan Constitution cannot be enforced, he'd respect those decisions and follow the rule of law," Murray said of Snyder.
While DeJong and Caspar were the first couple to receive a Michigan license, it was not the first same-sex wedding to occur in the state. Two men married a year ago during a ceremony at a northern Michigan Indian reservation after the tribal chairman approved a measure.
AP reporters Ed White, Jeff Karoub and Corey Williams reported from Detroit; Mike Householder in Ferndale, Mich.; and David Eggert in Lansing, Mich., contributed to this report.
- Romney, Huntsman may both be taking...
- Why we don't need to worry that Utah cities...
- At least 31 believed dead at Japanese volcano...
- Obama: US 'underestimated' Islamic State threat
- New mom Chelsea Clinton celebrates baby daughter
- Interracial marriages on the rise, but social...
- Game officials: Antelope poached near Casper
- US considers new offer to Iran at nuke talks
- Romney, Huntsman may both be taking... 33
- Republicans rallying behind religious... 32
- Obama: US 'underestimated' Islamic... 22
- White House: Holder resigning as... 20
- New mom Chelsea Clinton celebrates baby... 13
- Police: Fired worker beheaded Oklahoma... 11
- Tens of thousands of immigrant families... 10
- Congress releases war funds to fight Ebola 9