Ada

Formed December 22, 1864 (7^th county)

Ada County (494,694), Boise (235,712)

The Modern courthouse replaced a 1939 structure.  There was also an 1882 courthouse.  The current courthouse is on Front Street between 2^nd and 3^rd streets.  Front Street is United States Highway 20 through the city.  This structure was built in 2002 of red brick and concrete.  Lombard and Conrad were the architects.  A fountain and waterfall adorn the front of the structure.  The county was established on December 22, 1864 from Boise County as the 7^th county with Boise as the only county seat.  The daughter of a founder of Boise, Ada Riggs, is the source for the county’s name.  Boise gets its name from the river which reported was French for “wooded” river.  The French word is also the source for Boise County.  The Idaho state capitol is located in this county.  The county center is 12.4 miles South of Boise. 

Ada County government consists of a sheriff, a prosecuter, a coroner, a clerk, a treasurer, and an assessor (executive).  It has 3 Commissioners (legislative.)  Nine Circuit Court Judges and Nineteen Magistrate Court Judges serve Ada, Boise, Elmore, and Valley counties (judicial.) The county is located in southwest Idaho.  The Snake River forms its southern border.  The county is surrounded clockwise by Boise, Elmore, Owyhee, Canyon, and Gem counties. 

The area of the county is 1055 square miles.  It is 31 out of 44 in the state.  It ranks 1 out of 44 in population in the state.  It has a density of 469.2 persons per square mile making it 1 out of 44 in the state.  Ada County has 87.2% of its population in its incorporated areas.  Interstate Highway 84 crosses the county northwest to southeast from Canyon County to Elmore County.  United States Highways 20/26 enter the county from Canyon County and join Interstate Highway 84 to exit into Elmore County.  United States Highway 30 is joined with Interstate Highway 84 across the county from Canyon County to Elmore County.  The county’s shape is a capital letter F facing backwards.  Boise is in the northern quarter of the county.  Boise is the county seat and the largest city.  It is 47.6% of the county population.  The county seat is pronounced BOY-SEE.  This county is in the Boise City-Nampa Metropolitan Statistical Area.