Simplify the following text for a Grade 8 native English-speaking person.
Original: Approximately 15,000 people are estimated to have attended the ceremony , including the sitting governors of six of the 24 Union states : Andrew Gregg Curtin of Pennsylvania , Augustus Bradford of Maryland , Oliver P. Morton of Indiana , Horatio Seymour of New York , Joel Parker of New Jersey , and David Tod of Ohio .
Simplified: This included the governors of six of the 24 Union states . They were Andrew Gregg Curtin of Pennsylvania , Augustus Bradford of Maryland , Oliver P. Morton of Indiana , Horatio Seymour of New York , Joel Parker of New Jersey , and David Tod of Ohio .