Guns used to be banned inside the libraries, but spokeswoman Marilynne Gardner said that recently changed. Last year, the Supreme Court agreed with lower courts that cities, such as Seattle, have no right to ban guns in specific public places like parks and libraries.
Gun rights advocate Dave Workman said there's no reason guns shouldn't be allowed in libraries.
"Why shouldn't they? It's public property," he said. "Carrying a firearm is fundamental, individual civil right."
Seattle City Attorney Pete Holmes doesn't like the decision and said the Constitution has nothing to do with it.
"This is not a Second Amendment issue," he said. "It's important that everyone understands that."
Current laws ban guns from schools and courthouses, but lawmakers would need to amend the law if they want to keep guns out of libraries. Seattle officials don't think the votes are there in Olympia, so their hands are tied.
Library officials say they've never had an incident where someone tried to bring a gun into the library before, but they don't know what to expect now.
The original gun ban started in 2008 under then-Mayor Greg Nichols.