An investigation was carried out in Bankey Bazar block of Gaya and Rajauli block of Nawada districts in Bihar to assess the fluoride-contamination magnitude in groundwater and cultivated crops. The toxicological risk of fluoride exposure on three different age groups of the local populations has been measured. The groundwater was highly contaminated with fluoride (mean: 2.64 ± 1.8 mg/l) and alkaline in character (mean pH: 7.8 ± 0.38). About, 48.1 and 91% of the groundwater samples from Bankey Bazar (mean: 2.15 ± 1.78 mg/l) and Rajauli (mean: 3.2 ± 1.64 mg/l), respectively, cross the permissible limit of fluoride in drinking water. The major presence of fluoride in Bankey Bazar and Rajauli was confined at a depth range of 12.2–18.3 m (<0.5->8.0 mg/l) and 33.5–35.1 m (>1.5–8.0 mg/l), respectively and expected to be the hotspot territory in the regions. Mean fluoride concentrations in locally grown rice and wheat grain were found as 1.15 ± 0.81, 1.374 ± 0.667 mg/kg and 0.855 ± 0.226, 0.84 ± 0.186 mg/kg, respectively. Mean urinary fluoride concentrations of the studied populations were 10.4 ± 4.72 and 3.004 ± 1.97 mg/l, respectively. The cumulative EDI value for CTE and RME of the studied children was higher as compared to teenagers and adults. The hazard index (HI) for all the age groups residing in Bhaktuari of Bankey Bazar and Bhaunr, Phulwariya and Kachhariadih of Rajauli block was found much higher than the permissible limit (HI < 1). A good number of populations were suffering from dental and skeletal fluorosis. The life time non-cancerous risk (HILTNR) and probabilistic risk assessment based on fluoride exposure showed the potential threat among the residing populations.