According to findagrave.com Sgt James I. Mestrovitch was born on 22 May 1894 in/near Kotor, Montenegro.
His Medal of Honor information and citation is:
MESTROVITCH, JAMES I.
Rank: Sergeant
Organization: U.S. Army
Company: Company C
Division: 111th Infantry, 28th Division
Born: Montenegro
Departed: Yes
Entered Service At: Pittsburgh, Pa.
G.O. Number: 20
Date of Issue: 12/31/1919
Accredited To:
Place / Date: At Fismette, France, 10 August 1918
Citation
Seeing his company commander Iying wounded 30 yards in front of the line after his company had withdrawn to a sheltered position behind a stone wall, Sgt. Mestrovitch voluntarily left cover and crawled through heavy machinegun and shell fire to where the officer lay. He took the officer upon his back and crawled to a place of safety, where he administered first-aid treatment, his exceptional heroism saving the officer's life.
Source: www.cmohs.org/recipient-detail/2563/mestrovitch-james-i.php
Many thanks go to Don.Morfe, who provided all the information I needed to find this grave.