Trump currently has 83.7% of the vote.
Republican primary races are also being held in California, Montana, New Mexico, and South Dakota.
The real estate mogul clinched his party’s nomination last month after his last serious competitor, Ted Cruz, dropped out of the race.
This latest win comes in the wake of Trump’s controversial comments suggesting that the judge presiding over the hearing regarding his for-profit Trump University has a conflict of interest because of his Mexican heritage.
A number of Republican leaders have condemned the comments.