Minn. Stat. § 162.031

When a county state-aid highway route is so located that in order to achieve the designated objectives the commissioner determines that it is necessary to construct the highway across a portion of another county or state, the county initiating the construction is authorized to spend county state-aid highway funds for that purpose in the same manner as other expenditures for county state-aid highway purposes are made. No part of that highway may be constructed in another county until both counties approve the construction.