Samburu County Assembly passes the Building Bridges Initiative (BBI) Constitutional Amendment Bill Monday, becoming the 12 to approve the document.
The Bill was moved by 26 County Assembly members in a unanimous vote.
Other counties which have legislated the Bill include Siaya, Kisumu, Homa Bay, Busia, West Pokot, Trans Nzoia, Kajiado, Nairobi, Laikipia, Vihiga and Kisii.
Only Baringo County Assembly has opposed the Bill.
More than 10 counties were required to subject the bill to a vote Tuesday named Super Tuesday, including Machakos, Kitui and Makueni.
The Bill requires the approval of 24 counties for it to be conferred to both Houses of Parliament for consideration and thereafter be subjected to a national referendum.