ELECTIONS ACT NO. 24 OF 2011 (last amended in 2017)
4. Register of Voters
(1) There shall be a register to be known as the Register of Voters which shall comprise of—
(a) a poll register in respect of every polling station;
(b) a ward register in respect of every ward;
(c) a constituency register in respect of every constituency; (d) a county register in respect of every county; and
(e) a register of voters residing outside Kenya.
(2) The Commission shall compile and maintain the Register of Voters referred to in subsection (1).
(3) The Register of Voters shall contain such information as shall be prescribed by the Commission.
109. Regulations (1) The Commission may make regulations generally for the better carrying out of the purposes and provisions of this Act, and in particular, but without prejudice to the generality of the foregoing, may make regulations to—
(w) prescribe the procedure for voting for citizens residing outside Kenya;
See also IFES report:
"The Independent Electoral and Boundaries Commission (IEBC) requires that there must be at least 3,000 Kenyan citizens in a particular country for a polling station to be established. Eligible Kenyan members of the diaspora will only vote for the president. Although, they will also take part in any referendum, however, they will not vote for members of county assemblies, National Assembly representatives, senators, governors or woman representatives. For the 2017 elections, the IEBC conducted voter registration in Burundi, Tanzania, Uganda, South Africa and Rwanda."