Mont. Code Ann. § 19-3-401

(1) Except as otherwise provided in this chapter, all employees shall become members on of the defined benefit plan on first the first day of service. Each employer shall file with the board information affecting their employees' the employer's employees' status as members of the as retirement system 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 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 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 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 system. 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) Every employee who reenters service shall become Except as otherwise provided in this chapter, a member unless the of employee has had an original election of exemption from membership and either the employee's service was not interrupted by a break of more than 1 month. A seasonal defined benefit plan or the defined contribution plan is employee who has had an original election active member of exemption from membership is the system and is not subject to the requirement regarding the break in service while continuing in the employee's original eligible for employment and employed on a seasonal basis, but upon termination refund of employment to accept new employment contributions or absence of more than 1 month in returning to original employment in any ensuing season, for benefit payments if the seasonal employee shall become a member of the retirement system upon reentry. 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 service in determining eligibility district, the Montana school for membership under this chapter. 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