Favreau posted the following on his Twitter account.
Please stop asking if Harrison Ford is in Cowboys & Aliens. Okay? He is. Please don’t tell anybody.
Based on the Platinum Studios Comics graphic novel written by Fred Van Lente and Andrew Foley, the sci-fi Western explores what would happen if the traditional Old West enemies — cowboys and Native Americans — found the prairie attacked by aliens in mid-1800s Arizona.
The DreamWorks and Universal movie is targeting a July 29, 2011 release. Alex Kurtzman, Roberto Orci and Damon Lindelof wrote the script.
Source: Jon Favreau, Latino Review