The Wagoneers will be built at FCA's Warren Truck Assembly Plant in Michigan, which currently produces the Ram 1500. The overhaul required to add the Jeeps will also set the plant up to build Ram Heavy Duty models, which are currently made in Mexico. (It's not clear whether this would be additional Heavy Duty capacity or a complete move of production of those trucks to the US.)
The confirmed Jeep pickup will be built at the Toledo Assembly Complex in Ohio as expected. This is the same plant that builds Wranglers today and will produce the new JL Wrangler that the pickup version is expected to use.
All of these factory upgrades are part of a $1 billion investment by FCA. The retooling is scheduled to be completed by 2020, which means these models are likely to come online for the 2021 model year, which jibes with the rumors that the Wagoneers have been delayed. That the large Jeeps will be built at the plant that currently produces Ram 1500s also leads us to believe that they will in fact use a version of the Ram truck platform instead of being built off the Grand Cherokee platform as originally planned.
The timing of this announcement and its mention of Mexico and US jobs may have something to do with recent talk from President-elect Trump about US auto industry jobs and possible tariffs to be imposed on vehicles built across the border. Marchionne says these plans have been in discussion "for some time" but it's not clear what that timeframe was. Trump has targeted Ford, General Motors, and Toyota in recent tweets but has stayed quiet on FCA. While the announcement may have been political in nature, Jeep fans will no doubt welcome the news of the returning nameplates and the long-awaited pickup model.