Ledecky finished in 15:47.15 and was ahead of compatriot Kate Ziegler's 2007 world record of 15:42.54 through 800 metres before backing off, still beating second place getter Chloe Sutton by more than 20 seconds.
It was also the fastest time of the year and capped a great meeting, which doubled as selection trials for the Barcelona world championships from July 28-Aug.4, for Ledecky who also won the 400 and 800 freestyle titles.
"I was really happy with it," the 16-year-old told reporters. "It was a swim I was looking forward to all week. I just wanted to go out with a bang.
"I just wanted to swim a controlled swim, feel good and see what I could do and I'm looking forward to seeing what the U.S. can do in Barcelona."
Olympic champion Ryan Lochte claimed the men's 200 individual medley, also in the fastest time of the year at 1:55.44.
Lochte was ahead of world record pace but faded in the back half much to his disappointment.
"That's the story of this meet for me - going out fast and holding on for dear life," he said.
"I have four more weeks until worlds. Hopefully my legs won't be as tired."
Caitlyn Leverenz won the women's 200 individual medley.
Nathan Adrian won the men's 50 freestyle ahead of Anthony Ervin while the evergreen Natalie Coughlin won the women's 50 to qualify for her sixth world championships team.
- Sports & Recreation