From IRS Pub 970 (Chapter 8 on 529 Plans):
Eligible postsecondary school. An eligible postsecondary school is generally any accredited public, nonprofit, or proprietary (privately owned profit-making) college, university, vocational school, or other postsecondary educational institution. Also, the institution must be eligible to participate in a student aid program administered by the U.S. Department of Education. Virtually all accredited postsecondary institutions meet this definition. The educational institution should be able to tell you if it’s an eligible educational institution.
An eligible educational institution also includes certain educational institutions located outside the United States that are eligible to participate in a student aid program administered by the U.S. Department of Education.
https://www.irs.gov/pub/irs-pdf/p970.pdf
Bottom line: find out if the college is a 529 "Eligible Educational Institution" by being eligible to participate in a student aid program administered by the U.S. Department of Education.