Combine first 7 ingredients in a small bowl, stirring with a whisk. Place maple mixture in a large zip-top plastic bag. Add chicken thighs to bag; seal. Marinate in refrigerator 1 hour.
Preheat oven to 375°.
Remove chicken from bag, reserving marinade. Place marinade in a small saucepan over medium-high heat; bring to a boil. Cook until marinade reduces to 1/4 cup (about 5 minutes). Arrange chicken in a single layer on a foil-lined baking sheet. Baste with 2 tablespoons maple mixture; sprinkle evenly with salt. Bake chicken at 375° for 20 minutes. Turn chicken over; baste with remaining 2 tablespoons maple mixture. Bake 15 minutes or until chicken is done; sprinkle with onions.