North America’s biggest book sorter just opened in the Seattle area

Washington is home to Mount Rainier, the Space Needle, and the Super Bowl champion Seattle Seahawks. It’s also now home to what the King County Library System says is North America’s largest library materials sorter — a $5.2 million installation in Renton that formally opened Wednesday to handle the 25,000 items circulating through KCLS’s 50 libraries every day.

The new warehouse has been running since June 14. It’s the culmination of a more than three-year process. It replaces KCLS’s previous distribution center in Preston that operated for almost 25 years. Heidi Daniel, the organization’s executive director, said it was time to modernize: “It couldn’t keep pace with our growing community.” 

In 2025, KCLS’s 700,000-plus active cardholders checked out more than 11 million physical items and 12 million digital items. And while the previous sorter “served KCLS faithfully,” it was plagued by mounting maintenance needs and frequent breakdowns. “We were literally ordering parts off of eBay,” Daniel said.

KCLS said the new sorter can handle up to 8,000 items per hour at full tilt. 

Warehouse operations manager Charlie Mitchell walked through the sequence: drivers returning from branch pickups load totes onto one of two conveyor belts, and a pair of robotic arms at the far end destack them at a rate of one every 15 seconds. 

On an average day, Mitchell estimated that 800 to 900 totes could be received. A human worker scans each item individually, and that scan tells the system where the material goes next: onto a second belt and into one of 186 chutes where it’s packaged into a new tote for the next delivery run.

Rest assured, these books aren’t being destroyed after being scanned.

It took KCLS nearly four months to set up and install everything. The facility is run by a team of 13 people — six tasked with scanning library materials and seven who manage the back end, ensuring the new totes are filled and then setting them aside while they await delivery. 

When asked if it was challenging to train on the new equipment, Mitchell said no: “It’s a good job to pick up on.”

The clearest gains of this new setup, he said, are for the people working around the machine. Totes used to stack 14 levels high, sending workers up ladders to reach them; the new setup tops out at five, and instead of pushing totes down the line by hand, staff pulls them off onto a hand truck. 

The noise level dropped too. “The old system ran at about 89 decibels,” Mitchell said. “This [new sorter] runs at 67 decibels. It’s about the same as a vacuum cleaner.”

The other payoff shows up at the branches. Mitchell explained that the old sorter ran at 2 to 3 mph and put books in the wrong bin 1% to 2% of the time. While a low percentage, it sparked uncomfortable conversations with patrons who received an email saying their book was available for pickup. The new machine features automated tracking and destination redundancy support, likely reducing the odds of any mis-sorting.

King County Councilmember Steffanie Fain said the new facility solves a “major flaw” in the library system — at least according to her two young children: It will enable books to move through the system faster so people won’t have to wait as long anymore for the material they want to read, listen, or watch. 

“I’m not sure my kids have ever had an opinion about a distribution center before, but this one definitely has their full support,” she said.

“Today isn’t just about unveiling a remarkable piece of technology,” Daniel said. “It’s about investing in the future of KCLS, and most importantly, it makes a promise to the 1.6 million residents we are proud to serve: No matter where you live or which library you visit, you get the same selection, the same service, and the same speed.”