After rejecting four previous offers, workers accepted a wage increase and a US$6000 ($10,600) upfront payment.
The average annual base salary will increase from US$75,000 to US$109,000 at the end of the five-year collective bargaining agreement.
The Boeing machinists work on F-15 and F-18 combat aircraft, the T-7 Red Hawk Advanced Pilot Training System and MQ-25 unmanned aircraft in factories in Missouri and Illinois.
Union leaders had pressed for a higher bonus more in line with the US$12,000 received by IAM members in the Pacific Northwest last November, following a strike that lasted more than seven weeks.
The Seattle-area strike shuttered two major Boeing commercial airline manufacturing plants.
IAM representatives recognised they were unlikely to garner a similar bonus for midwestern workers in light of the higher cost of living in the Seattle region compared with St Louis, leading union representatives to push for US$10,000 during the talks.
Before the vote, IAM District 837 leaders recommended the latest proposal from Boeing.
-Agence France-Presse