Despite yields dropping to 0.66%, money market accounts at credit unions still contributed 55% to overall deposit growth, the latest industry data showed.

Over the past year, 61% of deposit growth was attributable to regular shares now yielding just 0.40%, according to CUNA Mutual Group's December Credit Union Trends Report, which tracked data through October 2010. Certificates of deposits at credit unions declined by 6.3% or $14.7 billion over the past year as rates paid fell 63 basis points to 1.29%.

Dave Colby, chief economist at CUNA Mutual, said when you add in share drafts at a 0.35% yield, you get 129% of all growth attributable to liquid deposits.

"The combination of deposit inflows going into low-yield, short-term accounts and rates paid declining for all account types, translated into a 56 basis point reduction in credit unions' cost-of-fund since October 2009," Colby said.

A fifth payroll Friday in October gave a significant boost to savings and asset growth, Colby noted. Still, these deposits are temporary as evidenced by the 3.1% month-only gain in share drafts, he added. At the end of October, total savings were up 4.4% year to date and 4.7% over the past year.