Santa Rosa-based American AgCredit, Sonoma County's largest financial institution, announced a deal Thursday to absorb Farm Credit Services of the Mountain Plains.

The merger with the Greeley, Colo., agricultural lender is American AgCredit's fifth since 2000.

The agreement, which took effect Jan. 1, makes American AgCredit the sixth-largest farm credit cooperative in the United States. It formerly was ranked seventh.

American AgCredit now has $5.58 billion in assets, an increase of slightly more than $1 billion due to the merger, and 400 employees, including about 60 from Farm Credit Services.

The Santa Rosa credit cooperative is the largest lender to Sonoma County's farmers, said senior vice president Terry Lindley.

Congress established the farm credit system in 1916 to provide loans and other financial services to farmers, ranchers, agribusinesses and rural homeowners.

American AgCredit, a member of that system, is owned by nearly 7,000 shareholders, each a borrower who owns a single share of stock valued at $1,000.

Lindley said the farm credit system has seen a trend toward consolidation because of the benefits of size.

"In today's world, you need to be as big a player as possible," he said.

The expansion, he said, will provide increased capital and more diversification in such crops as corn, cattle and hay.

The credit cooperative has been called American AgCredit since 2000, but the organization has existed in Sonoma County since 1933. It has 35 offices in California, Nevada, Colorado, New Mexico, Kansas and Oklahoma.