Koderma district occupies the northern end of the Chota Nagpur Plateau. The average altitude is 397 m above sea level. The topography is hilly and the area mostly has laterite soil with patches of clay. Although the net area sown is around 13% of the total area, Monsoon dependent agriculture supports majority of the population. Forest area covers 43% of the total area. Koderma Reserve Forest occupies the northern part of the district. Density of population in the district was 282 persons per sq km. Koderma district was once famous for its mica production but low quality of mica ore and high cost of production led to closure of many units. Only two units still survive. Around 40-50% of the families are below poverty line. Based on the number of households in 2011 census and BPL revision survey of 2010-11, the percentage of BPL families in the rural areas is 64.22%.
The Barakar River flows in the southern part of the district and supports the multi-purpose Tilaiya Dam. Poanchkhara, Keso, Akto, Gurio, Gukhana Nadi are the main tributaries of the Barakar in the district. The Sakri river is the main river in the northern part of the district. Ghggnna Naddi, Chhotanari Nadi are the tributaries of Sakri river.
Jainagar is located at 24°22′33″N 85°38′37″E.
Jainagar CD Block is bounded by Koderma and Domchanch CD Blocks in the north, Markacho CD Block in the east, Barkatha CD Block, in Hazaribagh district in the south and Chandwara CD Block in the west.
It is located 15 km from Koderma, the district head quarters.
Jainagar CD Block has an area of 183.37 km2. The block has 135 villages.
Gram Panchayats in Jainagar CD Block are: Beko, Chehal,chandrapur Dandadih, Gadgi, Gharaunja, Gohal, Hirodih, Jainagar East, Jainagar West, Kakorcholi, Kandrapdih, Kariyawan, Kathadih, Katiya, Khariodih, Naitand, Pipcho, Rupaidih, Satdiha, Tamal, Tetron, Tilokri and Yogiatilha.
As per the 2011 Census of India Jainagar CD Block had a total population of 131,279, all of which were rural. There were 67,708 (52%) males and 63,571 (48%) females. Population below 6 years was 24,519. Scheduled Castes numbered 19,527 (14.87%) and Scheduled Tribes numbered 239 (0.18%).
As per the 2011 census the total number of literates in Jainagar CD Block was 72,061 (67.50% of the population over 6 years) out of which males numbered 45,117 (82.08% of the male population over 6 years) and females numbered 26,944 (52.02%) of the female population over 6 years). The gender disparity (the difference between female and male literacy rates) was 30.06%.
As per 2011 census, literacy in Koderma district was 66.84%, up from 52.20% in 2001. Literacy in Jharkhand (for population over 7 years) was 66.41% in 2011. Literacy in India in 2011 was 74.04%.
Hindi is the local language in the Jainagar area.
21,483 wagons of coal were transported to Koderma Thermal Power Station in Jainagar CD Block in 2013-14. Banjhedih Thermal power plant is located here.
The Grand Chord line passes through this CD Block. There is a railway station at Hirodih.