Hillier returns to the Frontier League after a short stint with the Normal CornBelters in 2012. The Ohio native appeared in nine games for the CornBelters, yielding 13 runs on 18 hits and eight walks in 9.2 innings pitched. Hillier was signed by the Arizona Diamondbacks in February of 2013 after finishing 2-2 with a 5.40 ERA in 10 innings for the Palm Desert Coyotes of the California Winter League. He started in the Arizona Rookie League, finishing 1-0 with a 3.86 ERA in six games. The right-hander allowed just five runs on 10 hits and four walks in 11.2 innings while striking out 14. He held opponents to a .222 average and finished with a 1.20 WHIP. Hillier finished 1-3 with a combined 6.48 ERA in 33.1 innings between both the Arizona and Pioneer Rookie League. He struck out 33 and walked just 16 in 16 games total between the two teams in 2013. He was an infielder for Division-3 Thiel College in PA. and became a pitcher after breaking his hand, not able to grasp a bat but owning a mid-90's fastball.