I think I may have made a breakthrough ! I believe I found your grandfather Chelsea under Chalsie E. Ingersoll in the 1900 census. He was born Jan,1884 and was living with his uncle Jonathan.He was still 'at school' This Chalsie also had a brother William J.age 16 born 1883 living in the same household.
Here is the census record=
Name: Chalsie E Ingersoll Home in 1900: Cain, Fountain, Indiana Age: 15 Birth Date: Jan 1884 Birthplace: Indiana Race: White Gender: Male Relationship to Head of House: Nephew Father's Birthplace: Indiana Mother's Birthplace: Indiana Marital Status: Single Residence : Hillsboro Town, Fountain, Indiana Occupation: View on Image Neighbors: View others on page Household Members: Name Age Johnathan Ingersoll 56 Alfred E Ingersoll 21 Manchie R Ingersoll 19 William J Ingersoll 16 Chalsie E Ingersoll 15
=--= Name: Johnathan Ingersoll Home in 1900: Cain, Fountain, Indiana Age: 56 Birth Date: May 1844 Birthplace: Ohio Race: White Gender: Male Relationship to Head of House: Head Father's Birthplace: Ohio Mother's Birthplace: Ohio Marital Status: Widowed Residence : Hillsboro Town, Fountain, Indiana -=-=-=