The First Ohio General Assembly was the initial meeting of the Ohio state legislature, composed of the Ohio State Senate and the Ohio House of Representatives. It convened in Chillicothe, Ohio, on March 1, 1803, and adjourned April 16, 1803. This General Assembly coincided with the first year of Edward Tiffin's first term as Ohio Governor.

Under Ohio's first constitution, State Senators were elected to two year terms. For the first class, half were elected for one year and half for two years. Members of the House were elected for each term. The Constitution was written in November, 1802, and submitted to the U S Congress. Elections for the first session were held in January, 1803. The apportionment of legislative districts was based on the 1802 Ohio Constitution, in section 7 of the Schedule. Subsequent sessions would be elected each October, and meet the first Monday of December.

For the first session, the constitution apportioned four senators for Hamilton County, one senator for Clermont County, one senator for Adams County, two senators for Ross County, one senator for Fairfield County, two senators for Washington County, one senator for Belmont County, two senators for Jefferson County, and one senator for Trumbull County.

For the first session, the constitution apportioned eight representatives for Hamilton County, two representatives for Clermont County, three representatives for Adams County, four representatives for Ross County, two representatives for Fairfield County, three representatives for Washington County, two representatives for Belmont County, four representatives for Jefferson County, and two representatives for Trumbull County.

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