A drought in 1864 killed the livestock of Jose Antonio Sepulveda, forcing him to sell his coastal Rancho San Joaquin to Irvine and his partners.

In 1866 they purchased Rancho Lomas de Santiago from William Wolfskill; largely unfarmable due to its steep, hilly terrain, it had been used mainly as a sheep ranch.

[clarification needed] Unlike other early Newport Beach landowners, Irvine and his partners had no interest in subdividing and selling, intent, instead, upon identifying the most lucrative agricultural uses for their enormous 120,000-acre tract of land (49,000 ha).

When this auction was declared illegal, James II took over the reins of the ranch and accelerated efforts to increase its agricultural production.

In 1953, the National Scout Jamboree was held on Irvine Ranch land in the area of what is now Fashion Island Shopping Center.

During the early 1960s, the university and company, together with architect William Pereira, designed the Irvine Ranch Master Plan for developing the surrounding area.

[7] In 1977, a group led by A. Alfred Taubman and including real estate developer Donald Bren bought the company from the Irvine Foundation.

[8][9] The Bommer Canyon area was sold to the City of Irvine between 1981 and 1982,[5] purchased with grants obtained from the 1974 California Bond Act.

It encompasses almost one fifth of Orange County, from the Pacific Ocean and Newport Harbor, Laguna Beach, and Santa Ana Canyon, to the boundary of the Cleveland National Forest.

In August 2014, the Irvine Company announced plans to donate and preserve 2,500 additional acres of land previously approved for housing.