Mont. Code Ann. § 19-3-401

(1) Except as otherwise provided in this chapter, all employees shall become members of the defined benefit plan on the first day of service. Each employer shall file with the board information affecting their employees' the employer's employees' status as members as the board may require. An employee may become a member of the defined contribution plan only as provided in Title 19, chapter 3, part 21.

(2) A member of the defined benefit plan with at least 5 years of membership service who terminates service and does not take a refund of the member's accumulated contributions is an inactive vested member and retains the right to purchase service credit and to receive a service retirement benefit subject to the provisions of this chapter.

(2) (a) An inactive member of the defined benefit plan with at least 5 years of membership service is an inactive vested member and retains the right to purchase service credit and to receive a service retirement benefit subject to the provisions of this chapter.

(b) If an inactive vested member of the defined benefit plan chooses to take a lump-sum payment rather than a retirement benefit, the lump-sum payment consists of only the member's accumulated contributions and not the employer's contributions.

(3) A member of the defined benefit plan with less than 5 years of membership service who terminates service and leaves the member's accumulated contributions in the pension trust fund is an inactive nonvested member and is not eligible for any benefits from the retirement plan. An inactive nonvested member is eligible only for a refund of the member's accumulated contributions.

(3) (a) An inactive member of the defined benefit plan with less than 5 years of membership service is an inactive nonvested member and is not eligible for any benefits from the retirement plan.

(b) An inactive nonvested member of the defined benefit plan is eligible only for a refund of the member's accumulated contributions.

(4) A Except as otherwise provided in this chapter, a member of either the defined benefit plan or the defined contribution plan who returns to service within 30 days of is termination of an service is active an active member. Except as otherwise provided in this chapter, a member member of either the defined benefit plan or the defined contribution plan who terminates one service but remains in system and another service or is subsequently reenters service is an active member. not eligible for a refund of contributions or for benefit payments if the member either:

(a) returns to service within 30 days of termination of employment; or

(b) terminates one employment but remains employed in another position covered by the system.

(5) Time during which an employee of a school district is absent from service during official vacation is counted as membership service in determining district, the Montana school eligibility for retirement benefits. the deaf and blind, or a public institution of higher education is absent from service during official vacation is counted as membership service in determining eligibility for retirement benefits.

Membership -- – inactive vested members -- – inactive nonvested members