Neb. Rev. Stat. § 77-1813: Real property taxes; annual tax sale; return of county treasurer; when made; certified copy as evidence.

On or before the first Monday of April following the sale of the real property, the county treasurer shall file in the office of the county clerk a return thereon as the same shall appear upon the county treasurer's record, and such return, duly certified, shall be evidence of the regularity of the proceedings.