"It's time for Illinois to recognize the love and commitment of these couples," said John Knight, director of the Lesbian, Gay, Bisexual, Transgender Project of the ACLU of Illinois. "We've waited long enough."
Knight said Obama's comments, as well as Gov. Pat Quinn's backing of gay marriage earlier this month and nationwide polls showing increasing public support for same-sex marriage, set the stage.
The filings come a year after Illinois enacted civil unions, but many couples in the lawsuits said civil unions made them feel like second-class citizens.
Lambda Legal's lawsuit, which has 16 couples, includes Chicagoans Patrick Bova and Jim Darby. They've been together for 48 years and hope to marry by their 50th anniversary. They entered into a civil union last year, but said they want their relationship to be recognized in the same way as their heterosexual friends.
"I have bought so many toasters for so many weddings," Darby joked Wednesday at a news conference. "I want someone to buy me a toaster."
The 25 couples in both lawsuits tried to apply for marriage licenses in Cook County, but were denied.
It's unclear how Illinois will handle the cases' legal process, but attorneys with the advocacy groups are ready to take them to the state Supreme Court. The defendant named in the case, Cook County Clerk David Orr, is personally in favor of gay marriage. Several messages left for Cook County State's Attorney Anita Alvarez, who would represent Orr, were not immediately returned Wednesday.
A spokeswoman said Orr was out of the country and had not seen the lawsuit, but issued a statement on his behalf.
"The time is long past due for the State of Illinois to allow County Clerks to issue marriage licenses to couples who want to make that commitment," the statement said. "I hope this lawsuit clears the last hurdle to achieving equal marriage rights for all."
Currently, the District of Columbia and six states - Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont - have legalized gay marriage. Courts decided for gay marriage in Massachusetts, Connecticut and Iowa. A lawsuit, filed by Lambda Legal, challenging an Iowa law that barred gay marriage prompted the Iowa Supreme Court to legalize it in 2009.
Legislation to eliminate language that prohibits gay marriage is pending in Illinois, but a vote isn't expected before the session is scheduled to end this week.
Illinois' civil unions give same-sex couples some, but not all, of the same legal rights and protections as marriage, such as the power to decide medical treatment for a partner and to inherit a partner's property. When that law was approved last year, opponents - including some religious and conservative groups - said it was a step toward gay marriage.
Some opponents said that advocates were skirting what the public wants by taking the issue to the courts.