No county, regardless of population, and no municipality having a population of less than sixty thousand (60,000) persons according to the latest Federal Decennial Census shall be required to participate financially in the acquisition of lands for use for rights-of-way for state highways contracted for and constructed after the effective date of this section; provided, that this act shall not relieve any county or any said municipality, except those with a population of one thousand five hundred (1,500) or less, of such financial participation where responsibility for the same has been assumed under a preexisting contractual agreement with the department.
Okla. Stat. tit. 69, § 1206.1