Entrepreneurs purchased 64 small and mid-sized companies in Sonoma County during the first quarter, up 10 percent from a year ago, according to the BizBen Index.

But the total still lags below pre-recession levels and was 29 percent below the number of deals five years ago.

"This suggests that over the past five years, nearly one-third of the growing population of baby-boomer owners and others who wanted to sell their businesses have been unable to do so," said Peter Siegel, founder and president of BizBen.com.

Santa Rosa was the most active market, with 35 of the transactions in the quarter. Other active markets were in Healdsburg and Petaluma, where there were six deals in each city.