Ada County, Idaho: History
Ada County was created by the Idaho Territory legislature on December 22, 1864, partitioned from Boise County. It is named for Ada Riggs, the daughter of H. C. Riggs, a member of the legislature; he established the county and was a co-founder of Boise. Canyon County, which originally included Payette County and most of Gem County, was partitioned from western Ada County in 1891.