Groundwater is considered the primary source of water in many coastal areas. Increasing water demand leads to greater groundwater extraction, which results in a decline in groundwater levels and causes seawater intrusion. Balikpapan is a city at risk of seawater intrusion in its groundwater aquifer, especially in coastal areas that rely on groundwater as a source of clean water. This study aims to determine the extent and zones of seawater intrusion in the coastal areas of Balikpapan based on hydrochemical data from groundwater. Groundwater samples were taken from 19 dug wells and 8 bore wells along the coastal area of Balikpapan and then analyzed for their major ion content and evaluated using four geo-indicator methods: increased chloride concentration, Na/Cl ratio, Cl/Br ratio, Base Ex-change Indices (BEX), and Piper Trilinear Diagram plotting. The results show that increased Cl values indicate seawater intrusion in one dug well and 3 bore wells. The Na/Cl ratio indicates seawater intrusion in 4 dug wells and 5 bore wells. The Cl/Br ratio indicates seawater intrusion in 11 dug wells and 2 bore wells. The BEX indicates salinization in 2 dug wells and 5 bore wells. Based on the Piper trilinear diagram, 2 dug wells and 3 bore wells have groundwater facies of the alkali chloride type, with groundwater hydrochemistry dominated by alkali. Validating the geo-indicators with the Piper diagram, it was concluded that only one dug well and 2 bore wells were positively affected by seawater intrusion in the Balikpapan Timur and Balikpapan Selatan areas.